PDA

View Full Version : OT: Wiring a Workshop Need Advice



ckelloug
06-28-2007, 03:06 PM
Hi all,

I need to redo the electrical service at my house to run my new shop. After consulting with the electrical supply, they suggest a 320A continuous, 400A intermittent rated meter base with two integral disconnect breakers as service equipment. I'm planning on running a feeder from one 200A breaker to the shop's new panel and another 200A feeder off the other breaker to the house's old 200A panel.

The catch is I think I'm going to have to run the wires back to the house in Rigid or Intermediate Metallic Conduit so that it only has to be buried 6 inches and doesn't need to be concreted over. (My desire to dig around tree roots has run out after the sprinkler system. . .)

I wanted to double check here whether my plan to run the 2/0 copper 200A feeder from the service back to the house through 2 inch RMC sounded good.

Thanks in advance,

Cameron

pcarpenter
06-28-2007, 05:35 PM
You are able to get by with smaller entrance wire like that because of the short runs. I didn't know that back when I re-wired my old house and when doing the service entrance put in 3 3/0 entrance wires in 2" conduit. Suffice it to say it was about like trying to feed rebar through conduit.

I would think that would be fine....but probably overkill. I guess I don't know what your real shop needs are. However, I put up a 30x40 building a few years ago with a 100 amp service. With only one guy working (me) with about 30 Amps worth of overhead lights, the 220v air unit and the 220v air compressor running simultaneously, I figure I would still have to be able to weld with one hand and run the mill and lathe with the other to exceed 100 amps.:D

Paul

CCWKen
06-28-2007, 09:30 PM
I didn't know that back when I re-wired my old house and when doing the service entrance put in 3 3/0 entrance wires in 2" conduit. Suffice it to say it was about like trying to feed rebar through conduit.

I can relate to that. I did the same from the service pole to the house. Buried it 18" - 24" for about 150'. That's no easy task in this South Texas concrete they call soil.

The 2/0 seems a little small for a 200A service line unless it's a very short distance. But like PC said, you'd be a mighty busy fellow trying to use up 100A all at once. The Maximum Amps for power transmission uses the 700 circular mils per amp rule. While very conservative, it's a safe rule of thumb for underground or bundled wire.

Yankee1
06-28-2007, 10:46 PM
Hello Ken,
We used to call that soil Gumbo. You dig out a shovel full and try to throw it and it clings to the shovel. You brought back old memories.
Chuck

grand master flash
06-28-2007, 11:16 PM
2/0 copper or 4/0 alunimum is all that is required for 200 amp service. Generaly voltage drop is not an issue with small services because under most conditions there is not that much of a load on them. You will need a 4th wire for a equipment ground between the disconnect at the meter base and the panel and the NEUTRAL MUST FLOAT in the sub feed panels. With a disconnect at the meter base the panels become subfed and a floating neutrial is required and the neutrals equipment grounds are tied together at the service disconnect.

Grand Master Flash
WV Master Electrician

ckelloug
06-29-2007, 03:05 AM
Thanks to all and especially grand master flash! Despite being an engineer type, it's so much easier to get advice from people who do this kind of thing for real than to have to quintuple check one's own work.

The nominal usage planned is this: Miller Synchowave 250 dx :100 Amps 220V (plugged into fist sized Cooper Crouse Hinds 100Amp outlet from Ebay). L&L specialty Furnace Company GS1714 toolroom furnace 25A 220V. Lights Nominal. Birmingham 14x40 Lathe 20 Amps. Bridgeport with VFD 20A 220V. Air conditioning XX@ 220V some day. Look on electrical inspector's face: priceless.

Rigid conduit seemed the lesser of the evils than digging in tree root gumbo.

Oh goodie, off to acquire a gigantic pipe threading die for threading the conduit cuts. I assume conduit uses ordinary NPT threads, right?

Regards all,

Cameron

Forrest Addy
06-29-2007, 03:43 AM
First make sure your installation complies with local code and the NEC in all particulars. Second you don't HAVE to run 4/0:2/0 wire through 2" conduit. Moving up a size conduit makes installation so muck easier. Another trick is to lay out the wire along the ground and pass each length of conduit over it. MUCH easier than pulling it - especially if bends are involved.

Bends can be a real hassle also pulling ells. Use plenty of electrician's snot on the wire. I once did a buried service install tha required several bends to wind past a concrete dech and a well house. I had a contractor make me a few conduit bends on oversized dies. Made a real difference.

Edit. OOPS!!! Wiser heads than I pointed out that my lay it out on the ground trick is not to code which dictates the conduit runs have to be complete before pulling conductors. My apoligies to any who have been misled. Goes to show how reliable electrical information is on the internet and the need for all who solict it confirm it from expert sources before implementing it. My bad. I've done it many times and seen licenced electricians thread conduit on difficult runs in the past. I thought is was SOP. I should have looked it up.

pntrbl
06-29-2007, 03:57 AM
I did a 35 ft underground run to put some lights in a shed. With a bend at each end I couldn't get nothing thru it for the longest time. What finally worked was string and compressed air. It was amazing! The string was pulsing out the other end just as fast as SIL could put it in there.

Had a good laugh pulling the 3 wires later. The missus was pulling on the single wire I had pulled with the string. I was feeding at the other end. The black and white were on big rolls but I only had a 50ft for the green and all 3 were on a stick. 35 ft run. Should be fine. But pretty soon the green's almost gone?

The missus got to the 3 wires and just kept on pulling .....

SP

Todd Tolhurst
06-29-2007, 07:43 AM
Another trick is to lay out the wire along the ground and pass each length of conduit over it. MUCH easier than pulling it - especially if bends are involved.


Yes, very much easier, but also in violation of the NEC, which requires that the conduit system be complete before wire is installed.

wierdscience
06-29-2007, 08:49 AM
Yes, very much easier, but also in violation of the NEC, which requires that the conduit system be complete before wire is installed.

Yup and if it's PVC the glue will burn nice holes in the insulation.

I ran exactly one wire run in conduit too small,never again.Besides the larger the conduit the more stuff you can add later.My nieghbor once asked what size to run 80' from his house to his shop.I told him 3" would be good,4" better,he thought I was nuts but went with the 3" anyway.When he went to add a phone line,then cable tv,then he got the point.

Rusty Marlin
06-29-2007, 08:51 AM
Yes, very much easier, but also in violation of the NEC, which requires that the conduit system be complete before wire is installed.

shhhh! I won't tell if you don't.

I ran 150ft of 2/0 copper for 100 amps 220V to my shop. There was only one way to get that much wire through 2" conduit, by myself, with 4 90deg elbows and three 90deg Pvc Condulette Lb (I think that's what they are called).
Dug that mother trench 22" deep by hand too. Luckily we have soft sandy clay here.
I didn't run water or phone line out to the shop so I was able to ground rod it out there rather than run a 150' of solid ground wire too.

Evan
06-29-2007, 09:13 AM
Run it overhead on a messenger cable. Much easier.

J Tiers
06-29-2007, 09:56 AM
Yup and if it's PVC the glue will burn nice holes in the insulation.

I ran exactly one wire run in conduit too small,never again.Besides the larger the conduit the more stuff you can add later.My nieghbor once asked what size to run 80' from his house to his shop.I told him 3" would be good,4" better,he thought I was nuts but went with the 3" anyway.When he went to add a phone line,then cable tv,then he got the point.

That's another thing.....

Those are not permitted in the same raceway with 120/240 power wires......

ckelloug
06-29-2007, 10:50 AM
Rusty,

I think code says that there can only be 360 degrees of elbows between pull points.

As for the reason they want the wire pulled rather than assembled in the conduit , I suspect that it has to do with having the joints rotated with wire inside is more likely to score all of the way through the insulation than a single longitudinal scratch from pulling: just a guess.

I've got the 2002 NEC, and also the 2000 IRC (International Residential Code), which I believe is the one they're actually using for houses down here, and in fact the entire book set for a contractor's license. In those 3000 or so pages, there's a lot to forget when you don't do all of it every day.

Incidentally, the use of Rigid Metallic Conduit to avoid burying cables half way to China (deeper than 6") is specified in table 300.5 of my 2002 NEC. Bigger than 2" conduit isn't a real option for me because the service equipment I want to use has 2 inch knockouts in the directions I need to run the conduit. Electrical equipment in my experience, especially when it comes to grounding lug sizes and conduit knockouts, is usually sized to meet the requirements, not to allow for over-engineering.

Thanks for all the responses. I wouldn't have thought such a dumb question could have so many entertaining responses.

Regards All,

Cameron

pcarpenter
06-29-2007, 11:11 AM
You may save a bunch on a pipe die you may never use again. I needed a gentle bend added to myrigid entrance conduit installation at the old house and went to a local commercial electrical contractor/supply place. I paid a bit more for the conduit than I would have at Lowes etc., but they bent it and threaded the end either cheap or free. Certainly cheaper that buying a tool I would likely never use again.

I agree about going up a size whether you need it or not on the conduit. The exception is that if its in a very visible place on the house. It looks rather jakey to have what looks like sewer pipe running down the outside. On the other hand, maybe you can tell yourself it looks "commercial":)

Dittos on the "elephant snot" too. Use it *before* you skin the insulation off by dragging it over an ell corner or something (don't ask). Rigid metal conduit makes you realize why people love to use PVC. PVC is slicker in addition to being easier to handle.

Paul

Todd Tolhurst
06-29-2007, 11:04 PM
Rusty,

I think code says that there can only be 360 degrees of elbows between pull points.

Yup.


As for the reason they want the wire pulled rather than assembled in the conduit , I suspect that it has to do with having the joints rotated with wire inside is more likely to score all of the way through the insulation than a single longitudinal scratch from pulling: just a guess.

The primary reason is to ensure that the wire can be pulled through the conduit. One day, somebody may need to pull new wire through that conduit, and if the only way that can be done is by digging up and disassembling the whole shebang, well, that's not too good.

wierdscience
06-30-2007, 09:31 AM
That's another thing.....

Those are not permitted in the same raceway with 120/240 power wires......

Yup,but there is a saying around here-

"you can get them to follow the code some of the time,but not all of the time":D

Dawai
06-30-2007, 10:00 AM
Yes, following the code? When I was coming up, people burned down buildings till they learned what "not to do". A code book was way beyond most the alcoholics who wired buildings.

The union Apprenticeship program? Lots of the young guys don't appreciate the school. Most by the third year think they know it all. When they are gave the responsibility of "running" a small job, then they start really learning.

I ran several extra conduits in the ditch.. since I pulled computer network cable and a phone line into one.

I ran a one inch, Three #6's on a 50 amp breaker. I had a paint booth then and not a machine shop and paint booth. I have not upgraded yet. JUST that big compressor required a 50 amp service.

Pulling THHN or similar single conductor wire is mucho easier than trying to pull duplex or triplex or entrance cable.. MOST the mistakes I see novices attempt is to use the entrance cable in conduit. YOU actually need a 4 wire system if same codes as around here. Neutral, ground, two single phase hots..

I would be tickled with a 100 amp service to the shop. for another few years anyways. 200 amps, well the cost of the wire would make me rethink a meterbase out there. (actual local code) no external buildings shall be supplied by residential service. Only logic, since a fireman or other entering the building not familiar with the property lines would not know where to disconnect power. I really don't want a meter reader messing around my building thou. I caught one sneaking around the back yard looking at the 54 ford back there. I got posted-no tresspassing signs up, Evidently he just wanted to look and he had a reason he thought.

In the early 80s there was some wires sticking out of the sidewalk in front of ClarkLift of Dalton, I hunted for three days trying to find where they tied in to take them loose, Finally I got the bright idea to pump silicone in around the naked wires which had lost all thier insulation and put a junction box and concrete them over.. You could pull the wires into the conduit and weld, the ground sounded like bees, vibrating.. I see a hump in the sidewalk even today as I drive past. NO clue where them wires were fed from.

Even if you provide the safest wiring service by local code? Please follow up with all the internal wiring in your shop. I am as bad as anyone else to temporary things in. My paint shop side still has a light stringer.

ckelloug
06-30-2007, 10:25 PM
David,

Thanks for the admonishment and anecdotes. This is actually the second time I've rewired the service here. The first time was during my house rewiring which passed electrical inspection as one of the nicest homeowner wiring jobs the inspector had ever seen. The following is more detail than probably interests anyone but. . .

As to your comment about supplying two buildings from one service being forbidden, that is generally true by NEC but my anonymous chat with the inspection department indicates that they allow it and I believe that allowance traces back to exception 3 of NEC 230.40 which states "A single-family dwelling unit and a separate structure shall be permitted to have one set of service entrance conductors run to each from a single service drop or lateral". The inspection department here has permitted my building as a detached garage so they consider it part of the house more or less.

There is currently a 200A service running to the house on messenger wire from the pole that is kinda ugly and technically not code compliant although it is grandfathered by our local authorities since it dates back to 1943. My plan involves moving the service to the new garage shop about 30 feet away as the crow flies and then running 200A on 2/0 THHN Copper back to the house from the new meterbase. Since the long 200A circuit has to be pulled regardless, there's no reason not to put a 400A service on the new garage since it's only a few feet of wiring to make the garage 200A instead of 100. I'm planning to put a up a 400 A meterbase which has dual 200A overcurrent/service disconnects. Since the house is already set up for 200A, the 200A to the shop is just a matter of using an appropriate meter base.

I'm planning on pulling 3 2/0 and an insulated #6 for the ground from the new service equipment back to the house and doing the same to the shop. The meter base I will use is sctually a light commerical unit designed for 600A because it is what my local supply house carries and it has the bonus of having 1/0 grounding lugs which should keep the place nice and well grounded for the welder. The local electrical supply stocks 500 kcm copper so that's what I'll run from the service head to the meter socket.

Once I get into the shop, I'm going to wire everything with type AC on the surface of the concrete board walls because the last thing you want in a shop is to have wires buried where you can't get to them. (Also due to reasons I can't explain, several rolls of the stuff have accumulated in my back room and it's a way to use them up.)

I'm asking my questions here instead of another venue because it is fun to see what shop wiring stories everybody else has. It's also nice to get my reasonably carefully planned plan double checked. I have no intention of making an asshat of myself and goofing this up. You're talking to the man who installed arcfault interrupters in his bedrooms so far before their time that I had to explain what they were to the guys at the supply house. . .

Thanks again for all the comments. I should be putting up a tool bloat er... I mean gloat thread with pics as soon as this nonsense is finished, the inspection passed, and I don't have lathe parts in the middle of my living room.

Seeing no "What the gravy were you thinking posts", I guess I'll draw up the plans and go pull the electrical permit on Monday.

--Cameron

TECHSHOP
06-30-2007, 11:22 PM
But, what will the neighbors think?

Seriously, I think the one thing "we" have in common is a shop, be it small or large. I never think it "hurts" to ask about solutions to the more "common problems" like: storage, power, and shop layout. Sometimes it just keeps the echo chamber clear of "self intiatiated errors".

Deep in the process of "decluttering" and improving Studio G, where does all the money go...