Conductor size for 225a feeder

[petersonra]

I don't believe that is correct. There is nothing in 240.4(B) about load calculations.

not directly, but you are required to select the ampacity of the conductors IAW the load calculations, and the ampacity is the key.

 

[LarryFine]

Of course, if it is close enough you could just put in two large enough conduits to allow a 400 amp service to be run to it, and then leave the rest until a customer wants to get power...

The original service was 400a, which is why 4" EMT is there. We're extending the conduit to relocate the new panel, and we're sticking with the 4" to avoid reduction and to future-proof the installation, as it will be covered by drywall.

 

[don_resqcapt19]

I don't believe that is correct. There is nothing in 240.4(B) about load calculations.

But the feeder has to be sized per 215.2(A) and that does require a load calc. The round up rule does not change the conductor ampacity, it only permits the use of an oversized OCPD.

 

[david luchini]

not directly, but you are required to select the ampacity of the conductors IAW the load calculations, and the ampacity is the key.

And if the load is minscule, like for a feeder for future use?

But the feeder has to be sized per 215.2(A) and that does require a load calc. The round up rule does not change the conductor ampacity, it only permits the use of an oversized OCPD.

The Code doesn't preclude the use of the roundup rule when running a feeder for future use. The load could be maybe 30A on the feeder at present, when he's added the basic lights, receptacles and HVAC that he mentioned. The Code would allow a 205A conductor on a 225A OCPD in that case. The Code would prevent whomever comes along to fitout the space from exceeding the 205A ampacity of the feeder.

 

[petersonra]

And if the load is minscule, like for a feeder for future use?



The Code doesn't preclude the use of the roundup rule when running a feeder for future use. The load could be maybe 30A on the feeder at present, when he's added the basic lights, receptacles and HVAC that he mentioned. The Code would allow a 205A conductor on a 225A OCPD in that case. The Code would prevent whomever comes along to fitout the space from exceeding the 205A ampacity of the feeder.

240.4 (B) Overcurrent Devices Rated 800 Amperes or Less. The
next higher standard overcurrent device rating (above the
ampacity of the conductors being protected) shall be permitted
to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a branch
circuit supplying more than one receptacle for cord-and plug-
connected portable loads.
(2) The ampacity of the conductors does not correspond with
the standard ampere rating of a fuse or a circuit breaker
without overload trip adjustments above its rating (but
that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed
800 amperes.

The minimum conductor ampacity is determined by the calculated load. People don't always make a load calculation for this kind of thing, but it is required in a legalistic sense.

 

[david luchini]

The minimum conductor ampacity is determined by the calculated load. People don't always make a load calculation for this kind of thing, but it is required in a legalistic sense.

And if the calculated load is zero, eg, installing a feeder and panelboard for a future tenant, the Code would permit the feeder to use a 205A conductor protected by a 225A OCPD.

 

[Russs57]

Geez, you EC's must really get beat up on price/profit. I feel for you.

If I was the customer, and had any say, it would be at least 4/0, if not 250, copper THHN. You only pay once for doing it right.

 

[Cow]

If the OCPD is 225 amps, you have to use a conductor with an ampacity equal to or greater than 225 amps. That will required 300 kcmil AL.

This is what we'd run.

We're in a market where we don't have to run things down to the bare minimum just to get a bid accepted. That and a little common sense says 300 AL or 4/0 CU. But, aluminum is obviously at a much better ratio when you look at the dollars/amp.

 

[JFletcher]

Another option would be to use 200A fuses with the 250 MCM wire.

If we are going to preclude the use of 250 MCM with 225 amp fuses based on the premise that there is no load calculation, and the amperage could be above 205 amps, how do we know that a 225 amp subpanel is adequate? If the load was 231 amps, calculated or actual, then what?

What I am getting at is that if an inspector would not allow 250 MCM with 225 amp fuses because of no load calculation, why would he allow a 225 amp panel at all? 231 amps exceeds the 230 amp limit for aluminum 300 MCM, as well as the sub panel rating.

Article 215.2 (A)(1) seems to tell me that a load calculation must be done for feeders to determine their ampacity. An unbuilt retail space, final use to be determined, will have a minimum number of required receptacles and lighting. Any existing HVAC and exterior lighting and signage would be added up and give you a rudimentary load calculation.

And I am 99% sure of Larry's 99% that this most basic load calculation will result in an amperage of less than 205 amps and the ability to use 250 MCM with a 225 amp fused disconnect.

The final connected loads for whatever is built could be 35 amps could be a 135 amps. For the extra roughly $50 of wire and $0 of extra labor involved, I would go ahead and give them a 225 amp panel that can carry 225 amps.

Edited to add... I miss Don's post, number 23, and David's post right after... they said it much more succinctly than I did.

 

[LarryFine]

I do plan on using the 300mcm al wire. I had another thread earlier this year when the owner wanted to be able to supply 225a using 2" EMT before a redesign lowered the new ceiling height.

Yes, this project is more than six months old. :roll:

 

[electrofelon]

Are Y'all finding your supply houses stocking 300MCM? I dont recall ever using it. Of course you could always order it it, in which case Id do THHN colors.

 

[Cow]

Are Y'all finding your supply houses stocking 300MCM? I dont recall ever using it. Of course you could always order it it, in which case Id do THHN colors.

I doubt it, but like you, we'd just order it.

It sounds like Larry's job has been dragging on for quite a while, so lead time may not even be an issue.

 

[Strathead]

In code I have not seen too much except for the call for calculations, but since there is no tenant there are no loads to calculate, if I understand correctly.

So, if it was me, which it is not, I would size for the maximum the box can handle, which was stated as 225... then leave it for the tenant to finish up from there...
Because if I run it for 180 or for 195 and the next tenant needs 225... how do they get it?


Of course, if it is close enough you could just put in two large enough conduits to allow a 400 amp service to be run to it, and then leave the rest until a customer wants to get power...

I chose yours to comment on, not to argue directly with you, but because it segways in to what I have to say. Technically you could calculate lighting per the required amperage in 220 and however many receptacles are in there added along with any HVAC and use that even if it is only 100 amps or less. It is the on the tenant when they improve the space to ensure that the MOCP is enough to handle the NEW loads. Depending on the location, a restaurant with no gas, or a tanning bed salon could lease the space next week and need 400 or 600 amps.

So, as far as the OP's original question, there is no valid argument that the smaller conductor wouldn't be code compliant as installed. Now it all comes to what is conscientious. The OP didn't give the size of the space or the area that one could anticipate a likely tenant or if there are engineered plans and specs, what the actual wording is, so I don't think any of us can make a valid call with the information provided.

 

[kwired]

The Code would prevent whomever comes along to fitout the space from exceeding the 205A ampacity of the feeder.

+1

Unless there is an actual load of 206-225 amps it is nothing more then design issue to run 250 vs 300 MCM

The minimum conductor ampacity is determined by the calculated load. People don't always make a load calculation for this kind of thing, but it is required in a legalistic sense.

I've got many installs that don't have a load calculation or a very crude one, especially when it comes to a fairly minimal load on say a 200 amp service or feeder.

Geez, you EC's must really get beat up on price/profit. I feel for you.

If I was the customer, and had any say, it would be at least 4/0, if not 250, copper THHN. You only pay once for doing it right.

If I was customer and was more concerned about cost - it will be aluminum conductor. If I had other performance concerns it might be copper. If it were supplying sensitive equipment that don't like voltage drop issues, it might even be a larger conductor than what is being suggested here - depending on the details.

I do plan on using the 300mcm al wire. I had another thread earlier this year when the owner wanted to be able to supply 225a using 2" EMT before a redesign lowered the new ceiling height.

Yes, this project is more than six months old. :roll:

Most owners don't have a clue, if there is a 225 amp feeder breaker they have a 225 amp feed - even if you only ran 10 AWG copper for conductors.

If owner has his own electrical crew or maintenance crew with reasonable electrical knowledge, maybe you have better chance of them demanding full 225 amps of capacity, especially if that was in a set of plans/in a contract, design build - you weren't necessarily wrong.