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Axkiker
03-18-2017, 03:54 PM
So can someone help me understand why GFIC is required in a garage. I always thought GFIC was only used around water being I always saw them used in circuits in the bathroom / kitchen. What is the deal with requiring them in a garage ?

CPeter
03-18-2017, 04:07 PM
A garage is considered "outdoors" by code and therefore requires GFIC. The assumption is that you could leave the door open and plug in a long extension cord and go to a location similar to the kitchen or bathroom as far as electrical hazard goes.
CPeter

H380
03-18-2017, 04:09 PM
Water on the floor. Wet cars. Leaking water heaters. Extensions cord dragged out side and so on.

2008 NEC
210.8 Ground-Fault Circuit-Interrupter Protection for
Personnel. Ground-fault circuit-interruption for personnel
shall be provided as required in 210.8(A) through (C). The
ground-fault circuit-interrupter shall be installed in a
readily accessible location.
Informational Note: See 215.9 for ground-fault circuitinterrupter
protection for personnel on feeders.
(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-
ampere receptacles installed in the locations specified in
210.8(A)(1) through ( shall have ground-fault circuit interrupter
protection for personnel.
(1) Bathrooms
(2) Garages, and also accessory buildings that have a floor
located at or below grade level not intended as habitable
rooms and limited to storage areas, work areas,
and areas of similar use
(3) Outdoors
Exception to (3): Receptacles that are not readily accessible
and are supplied by a branch circuit dedicated to
electric snow-melting, deicing, or pipeline and vessel heating
equipment shall be permitted to be installed in accordance
with 426.28 or 427.22, as applicable.
(4) Crawl spaces at or below grade level
(5) Unfinished basements for purposes of this section,
unfinished basements are defined as portions or areas of
the basement not intended as habitable rooms and limited
to storage areas, work areas, and the like

dave_r
03-18-2017, 04:24 PM
Yeah, the floor in my garage is wet regularly for months at a time, generally from snow melting off my truck. I knock the big stuff off, from the mudflaps, but there's still enough to make a big wet spot.

MaxHeadRoom
03-18-2017, 05:00 PM
Outside or rough environments require a GFI, even when a power tool etc is double insulated, there could be a condition where water etc. could come in contact with the tool or equipment causing a danger to the operator.
Max.

Axkiker
03-19-2017, 01:28 PM
Well crap.... I created several circuits to make it a little easier for working on equipment etc and didnt think I needed GFI. Is there such a thing as a main GFI breaker I could just use to cover everything?

woodenbird
03-19-2017, 01:40 PM
Yes there is a breaker. Here is a link
http://www.homedepot.com/p/Square-D-Homeline-20-Amp-Single-Pole-GFCI-Circuit-Breaker-HOM120GFICP/100002959

Axkiker
03-19-2017, 03:56 PM
Water on the floor. Wet cars. Leaking water heaters. Extensions cord dragged out side and so on.

2008 NEC
210.8 Ground-Fault Circuit-Interrupter Protection for
Personnel. Ground-fault circuit-interruption for personnel
shall be provided as required in 210.8(A) through (C). The
ground-fault circuit-interrupter shall be installed in a
readily accessible location.
Informational Note: See 215.9 for ground-fault circuitinterrupter
protection for personnel on feeders.
(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-
ampere receptacles installed in the locations specified in
210.8(A)(1) through ( shall have ground-fault circuit interrupter
protection for personnel.
(1) Bathrooms
(2) Garages, and also accessory buildings that have a floor
located at or below grade level not intended as habitable
rooms and limited to storage areas, work areas,
and areas of similar use
(3) Outdoors
Exception to (3): Receptacles that are not readily accessible
and are supplied by a branch circuit dedicated to
electric snow-melting, deicing, or pipeline and vessel heating
equipment shall be permitted to be installed in accordance
with 426.28 or 427.22, as applicable.
(4) Crawl spaces — at or below grade level
(5) Unfinished basements — for purposes of this section,
unfinished basements are defined as portions or areas of
the basement not intended as habitable rooms and limited
to storage areas, work areas, and the like

So does this mean every circuit in a garage needs to have GFCI?? How are people doing this for high amperage circuits such as 220 compressor or welding stations? When I bought my house the garage came wired with a 15A circuit for lights, a 20A circuit with GFCI for outlets, and a 20A 220V for a welder. The only GFCI was on the receptacle circuit. It passed the inspection when I bought the house so I would have thought it would have been flagged if incorrect.

What am I not understanding here.

H380
03-19-2017, 04:07 PM
So does this mean every circuit in a garage needs to have GFCI?? How are people doing this for high amperage circuits such as 220 compressor or welding stations? When I bought my house the garage came wired with a 15A circuit for lights, a 20A circuit with GFCI for outlets, and a 20A 220V for a welder. The only GFCI was on the receptacle circuit. It passed the inspection when I bought the house so I would have thought it would have been flagged if incorrect.

What am I not understanding here.

2008 NEC
210.8 Ground-Fault Circuit-Interrupter Protection for
Personnel. Ground-fault circuit-interruption for personnel
shall be provided as required in 210.8(A) through (C). The
ground-fault circuit-interrupter shall be installed in a
readily accessible location.
Informational Note: See 215.9 for ground-fault circuitinterrupter
protection for personnel on feeders.
(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-
ampere receptacles installed in the locations specified in
210.8(A)(1) through ( shall have ground-fault circuit interrupter
protection for personnel.
(1) Bathrooms
(2) Garages, and also accessory buildings that have a floor
located at or below grade level not intended as habitable
rooms and limited to storage areas, work areas,
and areas of similar use
(3) Outdoors
Exception to (3): Receptacles that are not readily accessible
and are supplied by a branch circuit dedicated to
electric snow-melting, deicing, or pipeline and vessel heating
equipment shall be permitted to be installed in accordance
with 426.28 or 427.22, as applicable.
(4) Crawl spaces at or below grade level
(5) Unfinished basements for purposes of this section,
unfinished basements are defined as portions or areas of
the basement not intended as habitable rooms and limited
to storage areas, work areas, and the like

Axkiker
03-19-2017, 04:11 PM
2008 NEC
210.8 Ground-Fault Circuit-Interrupter Protection for
Personnel. Ground-fault circuit-interruption for personnel
shall be provided as required in 210.8(A) through (C). The
ground-fault circuit-interrupter shall be installed in a
readily accessible location.
Informational Note: See 215.9 for ground-fault circuitinterrupter
protection for personnel on feeders.
(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-
ampere receptacles installed in the locations specified in
210.8(A)(1) through ( shall have ground-fault circuit interrupter
protection for personnel.
(1) Bathrooms
(2) Garages, and also accessory buildings that have a floor
located at or below grade level not intended as habitable
rooms and limited to storage areas, work areas,
and areas of similar use
(3) Outdoors
Exception to (3): Receptacles that are not readily accessible
and are supplied by a branch circuit dedicated to
electric snow-melting, deicing, or pipeline and vessel heating
equipment shall be permitted to be installed in accordance
with 426.28 or 427.22, as applicable.
(4) Crawl spaces — at or below grade level
(5) Unfinished basements — for purposes of this section,
unfinished basements are defined as portions or areas of
the basement not intended as habitable rooms and limited
to storage areas, work areas, and the like


ahhhhhhh totally overlooked that.

H380
03-19-2017, 05:05 PM
ahhhhhhh totally overlooked that. I do it all the time.

vincemulhollon
03-19-2017, 05:39 PM
Is there such a thing as a main GFI breaker

By main you mean 200 amp service?

outlet GFCI $15 and you can daisy chain so the downstreams plain outlets are protected. Or used to be able to in the old days. Huge headache when an outlet trips off a whole circuit including your desk lights., but its cheaper...

110V 15 amp breaker $50 (note the slight price difference in buying a breaker vs one outlet)

220V 30 amp breaker $100 or so.

WRT a GFCI for an air compressor that $100 could save your life BUT there's much more likely ways to save your life before I'd drop that particular $100. A disconnect and lockout is even more likely to save your life and is cheaper, for example.

The biggest GFCI I've ever seen was 50 amps for I suppose a hot tub or something. I don't think 200 amp service input main breaker GFCIs are currently available. I don't think it would be fun to troubleshoot a whole-house GFCI.

I'm a little mystified how arc welder works on a GFCI if the work is grounded... isn't that almost the definition of when a GFCI should trip if just a couple mA of the current flow into the ground?

If you're going to GFCI any outlets in a shop for safety reasons even if not legally required I'd run the lights on a totally separate lights only circuit. It could be super dangerous if one of the GFCIs tripped out and took out the room lights while the lathe on a different circuit merrily spun away as you're fumbling around in the dark. This also comes up with overloads the only thing worse than setting my saw motor on fire would be killing the room lights because my saw motor is on fire. That kind of fumbling around in the dark turns it from a simple fire extinguisher event to whoops you dead from getting trapped and smoke inhalation.

Axkiker
03-19-2017, 06:16 PM
By main you mean 200 amp service?

outlet GFCI $15 and you can daisy chain so the downstreams plain outlets are protected. Or used to be able to in the old days. Huge headache when an outlet trips off a whole circuit including your desk lights., but its cheaper...

110V 15 amp breaker $50 (note the slight price difference in buying a breaker vs one outlet)

220V 30 amp breaker $100 or so.

WRT a GFCI for an air compressor that $100 could save your life BUT there's much more likely ways to save your life before I'd drop that particular $100. A disconnect and lockout is even more likely to save your life and is cheaper, for example.

The biggest GFCI I've ever seen was 50 amps for I suppose a hot tub or something. I don't think 200 amp service input main breaker GFCIs are currently available. I don't think it would be fun to troubleshoot a whole-house GFCI.

I'm a little mystified how arc welder works on a GFCI if the work is grounded... isn't that almost the definition of when a GFCI should trip if just a couple mA of the current flow into the ground?

If you're going to GFCI any outlets in a shop for safety reasons even if not legally required I'd run the lights on a totally separate lights only circuit. It could be super dangerous if one of the GFCIs tripped out and took out the room lights while the lathe on a different circuit merrily spun away as you're fumbling around in the dark. This also comes up with overloads the only thing worse than setting my saw motor on fire would be killing the room lights because my saw motor is on fire. That kind of fumbling around in the dark turns it from a simple fire extinguisher event to whoops you dead from getting trapped and smoke inhalation.

No I dont need a 200A breaker. My garage is only being fed with 60A so 60A or even a 50A main GFCI breaker would work. I guess I can just swap out the leading outlets on each circuit to protect everything down stream. I was just looking for a way around it as the square GCFI outlets wont work with the face plates I have. Yes yes I know stupid but I already had the stuff laying around.


Also im curious about something. Since not all of the outlets in my garage were on a GFCI circuit shouldnt it have failed the inspection ??

J Tiers
03-19-2017, 07:26 PM
...


Also im curious about something. Since not all of the outlets in my garage were on a GFCI circuit shouldnt it have failed the inspection ??

Yes. Unless any fell within the exceptions in the section as quoted above.

A good inspector would look around and if he sees a GFCI would still check any accessible outlets. A checker plug is not hard to make, and any thorough inspector should either have one, OR should trip the GFCI one by one, and verify that all outlets that are supposed to be GFCI are in fact GFCI protected.

There is SUPPOSED to be a sticker on any such to tell the user to go look at the GFCI if the outlet does not work. Some inspectors may assume that the sticker really means what it says.

flylo
03-19-2017, 08:43 PM
I didn't read the above but in out home only the 1st in a row of outlets had to be a GFI as it protected the rest in the line. It may have changed but does work fine.

RichR
03-19-2017, 10:57 PM
No I dont need a 200A breaker. My garage is only being fed with 60A so 60A or even a 50A main GFCI breaker would work. I guess I can just swap out the leading outlets on each circuit to protect everything down stream. I was just looking for a way around it as the square GCFI outlets wont work with the face plates I have. Yes yes I know stupid but I already had the stuff laying around.


Also im curious about something. Since not all of the outlets in my garage were on a GFCI circuit shouldnt it have failed the inspection ??

Hanging an entire breaker box off of a single GFI device is in my opinion a bad idea. It creates a situation where a ground fault in one branch circuit
takes out all the other branches even though there is nothing wrong with them.

J Tiers
03-19-2017, 11:23 PM
I didn't read the above .....

Yup..... and it shows.

pinstripe
03-20-2017, 07:52 AM
Hanging an entire breaker box off of a single GFI device is in my opinion a bad idea...

They have been a requirement here for many years. They do cause problems sometimes, but the breakers are downstream so you can isolate the faulting circuit. Our current house also has one for the lighting circuits, so I assume they are required for those now. Fridges are on their own circuit.

RichR
03-20-2017, 09:28 AM
They have been a requirement here for many years.
I know GFIs have been a requirement for a long time. I'm not aware of any requirement to feed an entire panel from a single GFI.

They do cause problems sometimes, but the breakers are downstream so you can isolate the faulting circuit.
In the mean time the whole box is dead so you might have to track done a flashlight first, possibly in the dark.

Fridges are on their own circuit.
Same in this country. All fixed appliances are supposed to be on their own circuits.

reggie_obe
03-20-2017, 09:39 AM
In the mean time the whole box is dead so you might have to track done a flashlight first, possibly in the dark.


One rechargeable battery powered emergency lighting unit would solve that problem.

pinstripe
03-20-2017, 09:50 AM
I know GFIs have been a requirement for a long time. I'm not aware of any requirement to feed an entire panel from a single GFI.

Correct, my reply could have been worded better. You don't have to have all outlets on one, but as that is the cheapest option... A better option is RCBOs where you get the RCD (GFI) and breaker in one unit. Each circuit then gets its own RCD/GFI.

A.K. Boomer
03-20-2017, 09:59 AM
In response to the OP, does not even take water on the floor of your garage, even just bare damp concrete is enough of a conductor to be of concern...

J Tiers
03-20-2017, 10:18 AM
Correct, my reply could have been worded better. You don't have to have all outlets on one, but as that is the cheapest option... A better option is RCBOs where you get the RCD (GFI) and breaker in one unit. Each circuit then gets its own RCD/GFI.

Actually, the better option is for each outlet have its OWN GFCI. That avoids having a problem shut down the entire circuit, which leaves you wondering where the problem is. With a GFCI at each outlet, the problem is obvious. And, since GFCIs are not immortal, you never have the entire circuit dead if the GFCI shoots craps.

Individual GFCIs are not in total much more expensive than the expensive breaker/GFCI unit. So the cost penalty is small, unless you have an awful lot of outlets on the circuit.

MikeL46
03-20-2017, 11:09 AM
My new shop has a GFCI breaker for the ground floor 120V outlets. The 230V outlets don't need protection (per the regs) even if the risk seems at least the same as the 120v outlets. The 2nd story has a wooden floor and does not need GFCI, nor did the lights. I did run everything in conduit (EMT).

Mike

lakeside53
03-20-2017, 01:54 PM
Don't try to run any 120v vfd on a gfci... they won't.

flylo
03-20-2017, 02:19 PM
Most all my cords are 10 ga with GFIs which add protection. I wouldn't do Main or any GFI breakers. Why don't 240v use GFIs? Because they don't have a ground & neutral?

rmcphearson
03-20-2017, 07:09 PM
So can someone help me understand why GFIC is required in a garage. I always thought GFIC was only used around water being I always saw them used in circuits in the bathroom / kitchen. What is the deal with requiring them in a garage ?

They are vital for spoiling a freezer full of meat while you are on vacation.

wombat2go
03-20-2017, 08:35 PM
Q's for those here that I see are more familiar with NEC than I am.
Q1:
My workshop here in Michigan is a room off the detached garage, built ( with 120V electricity) in 1951.
I have replaced the outlets with the polarized type, and checked the grounds.
I have added an isolator/ 10 Amp TD fuse unit to the outlets for lathe, table saw etc.

It does not presently have GFCI.
It is supplied via underground cable from a 20 Amp 10 KA 1 pole circuit breaker in the Couse Hinds panel in the house.
>>> Does this detached room with original wiring as updated, need GFCI to comply with NEC?

Q2:
My electronics bench is in the basement and is powered with 120 V
presently from an outlet connected to the original K&T ( knob and tube wiring screwed to the house wooden frame)
from 1926, no proper ground.
I have vintage test gear and i like to play around with small electronics, and also power electronics.
To make all this safer just for me in my retirement,... and I am not really looking to GFCI for this,
I am thinking to purchase for my bench outlets, a Hammond 171F.
This is a 115:115V 500 VA isolation transformer with tail plug and receptacle. (C UL & UL listed (File #E211544))
I would like to get an electrician in to install this properly, fed from the panel, to power an outlet strip above the workbench.

>>>> Will the electrician be able to install this in compliance with the NEC?

Thanks

lakeside53
03-20-2017, 08:44 PM
Most all my cords are 10 ga with GFIs which add protection. I wouldn't do Main or any GFI breakers. Why don't 240v use GFIs? Because they don't have a ground & neutral?

Because it hasn't been added to the NEC yet. The cast majority of residential is 120v; 240v is usually for dedicated appliances. They are much more concerned with you running extension cords outside from outlets.

240 still has a ground and you have 120 to ground.

lakeside53
03-20-2017, 08:51 PM
Q's for those here that I see are more familiar with NEC than I am.
Q1:
My workshop here in Michigan is a room off the detached garage, built ( with 120V electricity) in 1951.
I have replaced the outlets with the polarized type, and checked the grounds.
I have added an isolator/ 10 Amp TD fuse unit to the outlets for lathe, table saw etc.

It does not presently have GFCI.
It is supplied via underground cable from a 20 Amp 10 KA 1 pole circuit breaker in the Couse Hinds panel in the house.
>>> Does this detached room with original wiring as updated, need GFCI to comply with NEC?

Q2:
My electronics bench is in the basement and is powered with 120 V
presently from an outlet connected to the original K&T ( knob and tube wiring screwed to the house wooden frame)
from 1926, no proper ground.
I have vintage test gear and i like to play around with small electronics, and also power electronics.
To make all this safer just for me in my retirement,... and I am not really looking to GFCI for this,
I am thinking to purchase for my bench outlets, a Hammond 171F.
This is a 115:115V 500 VA isolation transformer with tail plug and receptacle. (C UL & UL listed (File #E211544))
I would like to get an electrician in to install this properly, fed from the panel, to power an outlet strip above the workbench.

>>>> Will the electrician be able to install this in compliance with the NEC?

Thanks

If it's detached.. today it needs its own ground rod AND a grounded conductor between the panels. But.. unless you modify it you are "grandfathered" to the code at time of install. Doesn't mean it's a good idea though!


Yes, any competent electrician can install this" to code". Remember.. to comply with NEC code you to have to have an inspection, so the AHJ (inspector) has the last word. None of this is difficult.

J Tiers
03-20-2017, 08:53 PM
For 500VA, I;d not bother wiring it in. Put a cord on it, and plug in. NEC does not cover plug-in equipment. UL does.

In fact, looking it up, they COME with a cord and plug. I knew that... seeing the item I realized I have one.

What I would do is install, or have installed, a proper outlet system, and not power things from a lashup of stuff off of one outlet in K&T wiring.

Your K&T is likely to be grandfathered, but I would assume that the panel is modern, probably a 200A panel with all the appropriate grounding etc. Spend the money getting some real outlets by your workbench. GFCI if need be.

Absent a proper grounding system, the electrician will have trouble putting in anything other than a GFCI protected outlet, which would meet code w/o an actual ground. But, YOU can install a GFCI, and it will be about as safe as anything else that would be done.

Overall, I think putting in "real" grounded outlets for your bench area is likely to be your best approach. They will have GFCI if that area is one covered by the NEC clause. You can still use the Hammond unit for powering the radios etc.

wombat2go
03-20-2017, 09:43 PM
Thanks to JT and Lakeside for the quick and informative replies.

Do you know what year the ground rod for detached room was mandated?
My workshop on the back of the garage is about 15 foot from the 4160V SWER with the 220 V pole transformer.
The house with the main panel is about 50 foot away and the 2 wire plus neutral/ground (3 wire overhead) goes from the pole to the house.

I would be reluctant to have a driven second ground rod in my shop, so close to that swer,
as my electrical boots are worn out
and I hope that would anyway be precluded by some code . (?)

For my electronics bench in the basement, I have about 12 outlets occupied and I could use 20.
Maybe I get electrician to add some outlets and do the isolation transformer and strip outlets myself. ..Thanks

Q3:
a lot of the wiring in this old house is K&T.
All that old K&T seems to be fed from one sub panel, fed from the ( later) Crous & Hinds main panel.

When I came here in 2001 from Australia I asked local electrician about AFCI ( Arc Fault Circuit Interrupter),
to feed the old K&T.
Electrician knew nothing about that.
At that time I read a lot of reliability problems with AFCI in USA.
>>>> How is it now ? Should I re-visit that?
Thanks & Regards

lakeside53
03-20-2017, 10:21 PM
AFCI are current code for bedrooms in most jurisdictions. They don't like brushed motors so vac cleaners and hair dryers can trip them.

Ground rod for detached building? heck.. a long time ago.... 70's or way before around here. Much more recent to require grounded conductor also.

You can get the 4160 located accurately likely for free. Have the Electrician drive the rod if you are chicken ;)

Any variance to code - call you local AHJ... only they can rule.

wombat2go
03-20-2017, 10:47 PM
LS, Thanks,
No need to locate, the 4160V pole and the swer ground rod is only about 15 foot from my lathe.
It is not driving the rod that is the problem,
it is the step potential in a fault event : Step Potential: Voltage between the feet of a person.

J Tiers
03-21-2017, 12:38 AM
If you are worried about the step potential, do what the powerco does in a substation.... Bury a metal mesh mat under the floor of the shed. Yes, could be an issue if you have already got a poured floor......

Alternately, you might be able to trench on the outside of the building, and bury a couple conductors that run around the building, as well as out to the sides. They should tend to act as "guard rings" to give you a reasonably constant potential island. If you can connect them to rebar in the slab that would be ideal. A row of rods driven in on 6 foot centers on the pole side would also help short any potential into the "ring conductor".

The good news is that he 4160 probably only has a fairly small fuse, unless it is a major feeder line. If it is a residential branch line it may have a small fuse of under 100A, and any step potential will be very transient and of a fairly low voltage.

The pole being nearby might be good, since the return may be through a neutral going to that ground, so yo would be lower potential. Or not.... we may have an earth return here, since the neutrals all appear local to the pole transformer secondary circuits, only one wire goes to our poles, and the 3 phase at the end of the block seems to have 3 wires only. I need to look at that again.

As for local ground rod, that depends where you are. Some places demand it, some seem to forbid it, unless it is something like a milking shed, where the NEC allows it to avoid a potential between equipment and local earth. Depends on how they interpret the "one service one earth rod" deal.

Driving two that connect to the same grounding conductor (EGC) but at a distance from each other can produce current in the EGC, which is a big no-no.

lakeside53
03-21-2017, 12:56 AM
I'm not really sure what the problem is. I have 4160 running 600 feet down my driveway to my transformer. Entire neighborhood is like that. The 45 year old concentric cable blows out a couple of times a year.... . half the neighborhood has been upgraded to schedule 80 conduit; the rest slated for next year. Mine just got done.

Get your local code from your local authority. They will give you the answers.

J Tiers
03-21-2017, 02:14 AM
The problem he is worried about is well known.

He has a pole, so it is an overhead line, open and able to short to ground if it falls.

If a high voltage line breaks and the live end grounds, there is current flow in the earth from the ground point to wherever it can exit the ground and re-enter the line, at a neutral, or another line, if two are down. That current flow produces a voltage drop in the earth.

With sufficient earth current, the voltage difference between your two feet can be a pretty high potential. This is mostly a problem in substations and especially power station switchyards, where 250,000 volts or more at a few hundred megawatts can produce some pretty spectacular potentials across earth.

With 4160 V, I'd not normally expect an issue. Even at 15 feet from the pole. My shed is virtually UNDER the 4160 branch up the block. about a metre off line in the back neighbor's yard. We do not have easements for the poles.

I assume Wombat has an easement, and is 15 feet off-line. If so, I think he is pretty much in the clear, even if he has an earth return. He could be closer.

1) If the grounded line lands directly behind his shop, and is also 15 feet from the return ground, the potential is not going to be too bad. Assuming generally constant resistivity, there will be a large potential in the first couple feet around the point of grounding, due to the high current density. That will use up a fair amount of the total potential.

The rest of it will be dropped across the remaining distance. The straight-line potential, NOT considering the "spreading resistance" but considering the straight line as a big resistor, would be about 277V per foot over 15 feet. In fact, it will be less, because the spreading resistance will eat up some at each end.

But the farther you get off-line, the lower the potentials will be. Starting from 4160V, and being 15 feet off line, I'd have to calculate the potential to be expected, and I don't want to right now. But it will be substantially lower than 277V per foot.

Now, if his shop floor is concrete, and has rebar in it, then he has a similar feature to the mesh under a substation. The rebar will tend to short out the earth potential, so the step potential is far lower on the concrete. Stepping off the cncrete on the side away from the line is likely to have some potential, but what that would be I have no idea without knowing a lot more about the dimensions, area and construction.

The farther away the break and the grounded line is, the lower the "step potential" will be. The ACTUAL potential may be higher. And if the local transformer shorts t the 4160, so hat the pole ground is hot, then the local potential culd be high, he could be in the spreading resistance zone, and there might be more of a potential until the fuse opens. But the rebar should help with that too. Especially if they cheaped out and instead of rebar, they laid reinforcement mesh... That would be really good, it would make the concrete have virtually the same potential all over.

I think it is a worry that can be safely ignored, due to the rebar and the relatively low voltage involved, unless Wombat has some extra info not supplied so far.

wombat2go
03-21-2017, 10:31 AM
I am not too worried, but I did some checking this morning.
Here is a rough diagram I did of the system here.
https://app.box.com/s/z49gfdn2ii6yxwt6q4dqn0le02rkm2j0
It looks like I had better check somehow that the fuse will open if the old 120 V motor on the lathe goes down to frame.

If there is an event on the 4160 -and a pole transformer did fail last week in the wind storm here.
-The power tripped and I heard the bang on the reclose.
There is some chance that the the concrete floor of the workshop would become alive with respect to frames my lathe etc

For example even if the ground voltage under the swer line only rose by 10%, that is 410 Volt.

I read a bit about SWER systems last night
Invented by a New Zealander for sparse rural areas
Common in Australia, New Zealand and Alaska, but not usually approved in main USA according to one refererence I saw.

But the system is all around the residential streets here in old Flint.