Article 626, design question

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Skubie

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Hi All,

(I also posted this over on the engineering thread before I saw the NEC topic - sorry for duplicating.)

The Article specifies a load factor of 0.2 for my climate zone, allowing for the cycling and indeterminacy of these refrigeration loads. My question is, where in the power supply does the load factor get applied?

Certainly, each branch circuit must be fully rated - 480V/30A. If I have 10 circuits, that's 300A. BUT, is my disconnect 300A or is it 60A (300A x 0.2 = 60A). How far upstream of the branch circuit can I down size my system according to the load factor?

Thanks for any answers on this, especially if you can cite a job in CA that was permitted and signed off.
 
Where did you find this load factor of 0.2 that you mentioned? I don't see any such thing in 626 (2014 NEC)

Next place to look is maybe art 220, but I don't find this there either but could have missed it. 626 is short enough it would be hard to miss.
 
kwired said:
Where did you find this load factor of 0.2 that you mentioned? I don't see any such thing in 626 (2014 NEC)

Next place to look is maybe art 220, but I don't find this there either but could have missed it. 626 is short enough it would be hard to miss.
Click to expand...

Thanks for the reply, kwired. I mis-stated the terminology. It's called the "demand factor" and it's in Table 626.11(B) in the 2014 NEC. The title of the table says "demand factors for services and feeders".

So ... Starting with my example of 10 each, 480V/30A receptacles (per 626.31(C)), at what point upstream does my system apply the 20% demand factor? I'm hoping it's at the panel disconnect.

{pause ... to actually read the code ... duh}

OK, 626.11(B) gives me the 20% DF. So looking under "feeders", am I reading Art. 220 correctly:
- Table 220.3 points back to my Art. 626 20% DF (under "electrified truck parking space", cool so far)
- My branch circuit load is not subject to 220 Sec. II (or Art. 430 for motor loads), it is specified in 626.31(C) as 480V/30A
- 220.40 (General) applies the DF to the service feeding the "service entrance" with a disconnect rated at 10 x 30A x 20%DF = 60A.

So, would I have a panel with 10-30A breakers, fed from a 60A disconnect?

I am not an electrician or the son of an electrician. Just trying to understand. ;-)
 
Just to throw a wrench into the works.

626.11 Feeder and Service Load Calculations.
(A) Parking Space Load. The calculated load of a feeder
or service shall be not less than the sum of the loads on the
branch circuits. Electrical service and feeders shall be calculated
on the basis of not less than 11 kVA per electrified
truck parking space.
Click to expand...

I might argue that no matter what the demand factor is you still have to use a minimum of 11 kVA per space, in this case about 13 A.

However, I only looked at it because I did not recognize the article number and was curious what it was for.
 
petersonra said:
Just to throw a wrench into the works.



I might argue that no matter what the demand factor is you still have to use a minimum of 11 kVA per space, in this case about 13 A.

However, I only looked at it because I did not recognize the article number and was curious what it was for.
Click to expand...

Thanks for jumping in. That refers to the 120/208 service for comfort loads in the truck cab. The 480V requirements are for the refrigerated trailer (TRU) and start in section IV, beginning with 626.30 and starts requirements that are in addition to those in 626.24(B). That much I figgered out. UGH!
 
jumper said:
Maybe OP means demand factor? IDK

Table 626.11(B) Demand Factors for Services and Feeders
Click to expand...

Either I completely missed that somehow or my E-book version of NEC was not working right when I looked before, I swear that 626 had less to it then then what I am seeing now:blink:
 
Skubie said:
Thanks for jumping in. That refers to the 120/208 service for comfort loads in the truck cab. The 480V requirements are for the refrigerated trailer (TRU) and start in section IV, beginning with 626.30 and starts requirements that are in addition to those in 626.24(B). That much I figgered out. UGH!
Click to expand...

where does it say that in the code?
 
petersonra said:
where does it say that in the code?
Click to expand...

My building depatment is having some of the same questions, so this is good. I'm hoping to get a read from the standard committee next week and suggest to them that they make some clarifying changes next revision. IMO, The code differentiates between the single phase branch circuits for "hotel loads" (626.10 f) and the 3ph circuits for TRU power (626.30 f) - some examples of the intentional distinction:

626.1 Scope.
The provisions of this article cover the electrical conductors and equipment external to the
truck **or** transport refrigerated unit that connect trucks or transport refrigerated units to a supply
of electricity, and the installation of equipment and devices related to electrical installations
within an electrified truck parking space.

IV. Transport Refrigerated Units (TRUs)
626.30 Transport Refrigerated Units.
Electrified truck parking spaces intended to supply transport refrigerated units (TRUs) shall
include an individual branch circuit and receptacle for operation of the refrigeration/heating
units. The receptacle associated with the TRUs shall be provided **in addition to the receptacles
required in 626.24(B).**

CA air regs will all but require TRU electrification starting in 2020 and racheting down to only 5 min run time allowed on diesel in 2030. So we need to understand this. In my climate zone with 20% DF, I definitely don't want to over design my system by a factor of 5.
 
petersonra said:
Just to throw a wrench into the works.



I might argue that no matter what the demand factor is you still have to use a minimum of 11 kVA per space, in this case about 13 A.

However, I only looked at it because I did not recognize the article number and was curious what it was for.
Click to expand...

The 11 kVA is the 208V/50A circuit breaker for the parking space electrification. It has the following receptacles:
1 ea., 208V/30A
2 ea., 120V/20A
As called out in 626.24(B) (1) & (2) - the exception would allow this to down rate the branch to just 5 kVA.
 
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