Service Feed Size

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We been called down on this before.I am looking at 90 degree colum and geting 205 for 4/0 time 2 = 410 then drerating at 80% for 4-6 conductors and getting 328.The calculated load would be a joke at this point because we dont even have a tenant.
 
Jim W in Tampa said:
We been called down on this before.I am looking at 90 degree colum and geting 205 for 4/0 time 2 = 410 then drerating at 80% for 4-6 conductors and getting 328.The calculated load would be a joke at this point because we dont even have a tenant.
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If you can not produce a calculated load how was the size chosen?

If you can not produce a calculated load maybe the inspector will require protection at 328 or less. :p

BTW what type insulation and is it in a wet location?
 
I would not have a problem with it at this stage of the project, with no tenant what else can you do but guess
 
iwire said:
If you can not produce a calculated load how was the size chosen?

If you can not produce a calculated load maybe the inspector will require protection at 328 or less. :p

BTW what type insulation and is it in a wet location?
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xhhw ,is there any allowance for next breaker size (350)
The engineer used typical loads 3 ac units,water heater ,frig,lights as per print but thats changed.No way to really figure what will be pluged in so 180 per yoke.I am finishing what was already started and if this wont fly then we have 2 buildings with all the wire pulled.Original specs were 400 copper x3 and 350 amp breaker,but that was not followed.
 
mpd said:
jim w

does the engineer know his or her design was changed?
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Shhhhh.Often we change things to please ourself and get our own engineer to stamp it.Customers often wave the original for cheaper price on what we suggest.Not saying its right but thats how it goes here.
 
Jim W in Tampa said:
I have a situation of 2 sets of 4/0 aluminum in 1 conduit. My calculation was max amps after derate is 328. Could i use a 350 mdp breaker?
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iwire said:
BTW what type insulation and is it in a wet location?
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Jim W in Tampa said:
xhhw
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Still wondering if it is a wet location?

Jim W in Tampa said:
My calculation was max amps after derate is 328.
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Lets say it is a dry location

T310.16 shows 4/0 AL XHHW having rating of 205 amps.

205 * 2 = 410

410 * .8 = 328 amps.

Jim W in Tampa said:
Could i use a 350 mdp breaker?
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Yes....providing the load does not exceed 328 amps.

You say this is a service so we have to follow Part VII of 230.

230.90(A)(1) Exception 2 tells us we may use 240.4(B) and 240.6

Now lets say it is a wet location and it is not 'type -2' XHHW

In that case the T310.16 rating is only 180 amps

180 * 2 = 360 amps

360 * .8 = 288 amps.

That would limit you to a 300 amp breaker.


Now keep in mind none of the above changes the actual ampacity of the conductors or the service rating.

You service will have a rating of 328 or 288 amps regardless of the increased breaker sizes allowed by 230.90(A)(1) Exception 2
 
Jim W in Tampa said:
It is wet and is xhhw-2
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So 328 amps it is, just as you thought.

So a 350 OCPD could be used.

Why not run two sets of 300 AL in the same raceway for a true 400 amp service?
 
iwire said:
So 328 amps it is, just as you thought.

So a 350 OCPD could be used.

Why not run two sets of 300 AL in the same raceway for a true 400 amp service?
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Wires are already pulled so gotta use whats there.My concern is that others will add to this load and never even think about the total
 
I agree..

I agree..

Jim,
I agree and from an inspectors point of veiw I don't like it either but can't red tag it. As long as the next guy pulls a permit and has a sharp inspector.... well, you get the idea!
 
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