200A Service in 1-1/4" RMC?

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DaveTap

Senior Member
Location
Currently Flowery Branch, GA
I have to upgrade an existing 100 amp residential panel in NW Chicago suburbs to 200 amps and I'd really like to use the existing 1-1/4" service riser because it is buried inside of the existing barn style roof.
Table 310.15(B)(6) says the 200 amp service could be 2/0 copper and Table C.8(A) allows three 2/0 Compact Conductors in 1-1/4" RMC.
Local inspector says it has to be 2" RMC because ComEd requires it but ComEd says there is no such requirement.

Is there anywhere in the code that states this service must be a 2" conduit or is it acceptable to re-use the existing 1-1/4" drop?
 
cowboyjwc

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
You need 1 1/2 conduit for a 200 amp service, well actually you need 1 1/2 for three 2/0. Some utilities require a 2", but it's not in the NEC.
 
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david

Senior Member
Location
Pennsylvania
Your utility should have this information in a pamphlet available on line. Here our utility does have requirements to the min. size of a riser that they will connect a service drop to.
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
DaveTap said:
I have to upgrade an existing 100 amp residential panel in NW Chicago suburbs to 200 amps and I'd really like to use the existing 1-1/4" service riser because it is buried inside of the existing barn style roof.
Table 310.15(B)(6) says the 200 amp service could be 2/0 copper and Table C.8(A) allows three 2/0 Compact Conductors in 1-1/4" RMC.
Local inspector says it has to be 2" RMC because ComEd requires it but ComEd says there is no such requirement.

Is there anywhere in the code that states this service must be a 2" conduit or is it acceptable to re-use the existing 1-1/4" drop?
Click to expand...

As others said, NEC is OK in general. Many POCOs have a 2" minimum but some will allow smaller where the riser is not the attachment point of the drop.

But I think the biggest problem is where do you get CU compact? I'm sure it's made, but I have never seen it.
 
Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
You can two 2/0 and reduced neutral. It will work fine for 1.25" conduit.
 
Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
DaveTap said:
That's what I thought, I just wanted to be sure and of course have some backup ammunition for the inspector tomorrow.
Thanks Guys:D
Click to expand...

1.25" is allowed unless it is local amendment or your local PPOCO requirement.

Your AHJ may ask for a detailed load calculation in order to approve the reduced neutral.

Also, you can do IMC with three 2/0 copper.
 
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DaveTap

Senior Member
Location
Currently Flowery Branch, GA
edward said:
1.25" is allowed unless it is local amendment or your local PPOCO requirement.

Your AHJ may ask for a detailed load calculation in order to approve the reduced neutral.

Also, you can do IMC with three 2/0 copper.
Click to expand...

Well in this case I can't do IMC without ripping open the roof so I'll get the compact conductors and stay with full size neutral even though the reason for this upgrade are the 240V welder, mill, lathe, and bandsaw in the new garage. That is assuming I can convince the inspector to allow it.
 
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Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
DaveTap said:
Well in this case I can't do IMC without ripping open the roof so I'll get the compact conductors and stay with full size neutral even though the reason for this upgrade are the 240V welder, mill, lathe, and bandsaw in the new garage. That is assuming I can convince the inspector to allow it.
Click to expand...

You don't need any compact conductors for the reduced neutral. As long as your calculation shows smaller neutral then you can use the 1.25" RMC.

The compact is probably more expensive than the regular and I don't know if they are made in copper.
 
kwired

kwired

Electron manager
Location
NE Nebraska
DaveTap said:
Well in this case I can't do IMC without ripping open the roof so I'll get the compact conductors and stay with full size neutral even though the reason for this upgrade are the 240V welder, mill, lathe, and bandsaw in the new garage. That is assuming I can convince the inspector to allow it.
Click to expand...
The more 240 volt load you have the better chance you have of being able to reduce the neutral as those 240 volt loads are taking away from what is left to potentially utilize the neutral. For simplicity take your 200 amp base and subtract the 240 volt loads - especially if they are loads that get demand factors of 100% applied in load calcs. If you can subtract say 50 amps (not impossible at all if you have electric heat or water heating) that only leaves you with 150 amps of possible loads that could utilize the neutral, so in that case you should never need more then a 150 amp neutral conductor without even going through the process of determining just how balanced your neutral loads are.
 
kwired

kwired

Electron manager
Location
NE Nebraska
ActionDave said:
Why the strong affection for the full size neutral?

I can count on one hand the number of full size service nuetrals I have pulled and have fingers to spare. None of them were for a house.
Click to expand...

Inspectors around here generally let you reduce neutral two conductor sizes (for anything 100 amp or over) without wanting to see how you calculated the size you used or where it is otherwise obvious the neutral load is minimal.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I have not seen a drawing or detailed description from the OP, but that note applies only when the service riser provides the mechanical support for the messenger wire. It does not apply if the mechanical load is transferred to a wall or roof bolt or plate.
 
F

fmtjfw

Senior Member
Location
Fairmont, WV, USA
If you can find 600-1000V compact CU, please tell us where.

The only compact CU I have seen is in HV cable, because it has a smaller diameter, it takes less insulation than non-compact CU.
 
kwired

kwired

Electron manager
Location
NE Nebraska
You can run 4" RMC if you want, it still isn't any stronger then what it is fastened to. 2 inch is plenty strong enough if well fastened and the drop isn't too long or heavy. If there are large tree limbs hanging over the drop - it doesn't matter how heavy the mast is - something is likely going to break if that limb ever falls. If anything POCO should refuse to connect a drop when there are tree limbs that threaten the line.
 
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