Conduit size

[AZ Contractor]

I am beginning a TI on a Sushi restaurant and the conduit size on the plans do not match the conduit size at the site. The plans state that there are 2 1/2" conduits for my electricians to pull their lines with when in fact the conduits are only 2".

My electrician called the engineering firm that did the plans and one engineer stated that 2 1/2" conduits are required. My architect called the same engineering firm and another engineer told him that 2" was sufficient.

I hope I'm gong to explain this part right but my electrician speaks with a heavy accent and I think this is what he said he's going to pull in the conduit are 4 - 4 OD wires and a #6 ground. What size conduit is required for those wires?

On a side note I left a message with the engineer that said 2" was ok and if he in fact states the same thing to me I'll have him put it on paper and stamp it.

[jwelectric]

What kind of conduit and what kind of wire?

On a side note, if the electrician that you have hired to do the installation does not know how to size the conduit to the conductors then maybe you should start thinking about a different electrician.

[littlebluetruck]

Originally Posted by AZ Contractor

my electrician speaks with a heavy accent and I think this is what he said he's going to pull in the conduit are 4 - 4 OD wires and a #6 ground...

4/0!! lol!

[AZ Contractor]

Hey wise guys, my electrician is the one that said its not going to work and the engineering firm is the one that can't get there facts straight. He is competent as are all of my subs.

PVC conduit
4#3/0
1#6 bond

[stamcon]

Andre, the conduit size depends on the wire type. If the conductors are THHN, THWN OR THWN-2, a 2" conduit is the minimum. If TW, THHW OR RHW, then 2½" conduit.

steve

[jwelectric]

Andre

Thank you for the compliment. I had rather be a wise man than a smart man.

In my state as well as the beautiful state of Arizona it is on the electrical contractor to install a compliant system whether the engineer or architect has enough sense to design a compliant system or not.

As has been pointed out the insulation and conductor type will make a huge difference in the size of the conduit. If the PVC is schedule 40 or 80 will make a difference also.

From page 628 of the NEC we find that a 2” Schedule 80 PVC conduit with over two conductors has a maximum fill of 1.15 inches and a 2 ½ Schedule 80 has 1.647.
Page 629 gives us the fill for a Schedule 40 PVC and we find 1.316 and 1.878 respectfully.

Conductors can be found on the following pages. Type THW having an area of .0726 for#6 and .3117 for 3/0.
Type THHN having an area of .0507 for #6 and .2679 for 3/0.

This will give a minimum fill of .8544 for THHN conductors and 1.0077 for THW conductors.
As you can see either of these conductors will fit into a 2 inch PVC conduit of either Schedule 40 or 80 although pulling the THW conductors in a 2 inch PVC will be a chore at best.


Now call your engineering company and tell them that you have had this done for free and they need to find another program to run their conductor fill with that they charge an arm and a leg for.

Have your electrician drop me a check in the mail for doing for you the job that he should have done for you.

If the specs for the job calls for a 2 ½ inch conduit then send the 2 inch back and have it replaced with 2 ½ inch as mandated by the job specs. These specs are what were approved by the planning department therefore what they mandate is what is to be installed as long as they meet or exceed the requirements of the NEC.

Maybe George will run these through one of his programs and we can compare his findings with those of your engineer.

[AZ Contractor]

Originally Posted by jwelectric

If the specs for the job calls for a 2 ½ inch conduit then send the 2 inch back and have it replaced with 2 ½ inch as mandated by the job specs. These specs are what were approved by the planning department therefore what they mandate is what is to be installed as long as they meet or exceed the requirements of the NEC.

Mike,


The shell contractor installed the 2" conduit underground and it runs about 100' under slab. There is no 'taking it back'.

The engineering firm screwed up. They called out that the existing conduit size was 2 1/2" when in fact it was 2". So instead of tearing anything out or returning anything, I'll make the architect call the engineering firm and run some calcs on the conduits and state that the 2" PVC is ok, if in fact it is, and submit it to the planning department so the city does have this on file.

Thanks for your reply.

[jwelectric]

Sometimes people say things that they don’t know that they are saying when saying them.

Originally Posted by AZ Contractor

Mike,
The shell contractor installed the 2" conduit underground and it runs about 100' under slab. There is no 'taking it back'.
Thanks for your reply.

Here you have told us that the conductors will be required to be listed for a wet location as outlined in
310.8 (C) Wet Locations. Insulated conductors and cables used in wet locations shall be
(1) Moisture-impervious metal-sheathed;
(2) Types MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THHW-2, THWN, THWN-2, XHHW, XHHW-2, ZW; or
(3) Of a type listed for use in wet locations.

Installing either of these conductors sized as you outlined for the distance you have outlined will be a major chore in a 2 inch PVC conduit.
My prayers are with the people assigned with the pull.

[stamcon]

Mike, the post stated "4 - 3/0 and 1 - #6". This would be 1.3194 for THW and 1.1223 for THHN. 2" SCH80 wouldn't work for the THW condctors.

steve

[jwelectric]

Originally Posted by stamcon

Mike, the post stated "4 - 3/0 and 1 - #6". This would be 1.3194 for THW and 1.1223 for THHN. 2" SCH80 wouldn't work for the THW condctors.

steve

Thanks for pointing out my mistake, I missed the boat on this one.

[George Roberts]

AZ Contractor ---

While the plans show 2-1/2" conduit someone made a mistake and the 2" conduit has been approved by the engineers. (This explains why you got different answers from different engineers.)

I expect the engineer who said 2" was sufficient looked at the manufacturer's data. One looks there for wire sizes not the NEC.

Your electrician should heve no trouble in pulling the wires in the conduit.

[jwelectric]

Originally Posted by George Roberts

I expect the engineer who said 2" was sufficient looked at the manufacturer's data. One looks there for wire sizes not the NEC.

George
I know in my heart that you mean well with some of your post but sometimes I can’t help but wonder where you come up with your answers.

If these conductors are the service entrance conductors or are feeders for a sub panel, how would the manufacture’s listing tell us anything about how to size the conductors?

I agree that the branch circuit conductors supplying the piece of equipment would sized according to the manufactures suggestion, but the service entrance or feeder conductors MUST be sized by the NEC.

Even if the engineer looked at the name plate of the equipment it would only give the load in volt-amperes or amperage and not the wire size so where do you look to find out what size wire to use?

Now some of the things that I know about this installation are:

Originally Posted by AZ Contractor

PVC conduit
4#3/0
1#6 bond

Mike,
The shell contractor installed the 2" conduit underground and it runs about 100' under slab. There is no 'taking it back'.
Thanks for your reply.

This is a new installation and it is being supplied by three phase rated at about 200 amps. If this is a single piece of equipment then it is one hell of a piece of equipment to be found in a Sushi restaurant. Maybe it is an electric boiler or something like that. What ever this piece of equipment is it will cost over $40 an hour to operate (based on my kwh rating).

There is one thing that I have learned in this forum and this thread backs me is:
A lot of engineers can make a mistake but, A engineer can make a lot of mistakes.