I would like to start a discussion regarding CEC demand factors for load calculations vs. NEC demand factors.
From what I can derive (from Section 8), the CEC does not allow much in the way of diversification. For example, in a commercial kitchen the NEC allows diversification in regards to kitchen equipment loads, such as ranges, whereas the CEC requires 100% of the nameplate rating.
Does anyone have any thoughts on loading the secondary of a transformer based on CEC load calculations vs. NEC load calculations?
It might help if you can ask specific questions. It's tough to make a comparison unless someone has knowledge of both codes.
I assume your commercial kitchen is in a restaurant. Otherwise it isn't specifically dealt with in our code. See Table 14. What you say about 100% of nameplate rating is generally true in non-residential settings.
twh, thanks for your response. You are correct, our commercial kitchen is in a restaurant.
HotLine1, thanks for the welcome.
I'll provide some more resolution to the specifics of the situation we are facing. We are renovating an existing commercial restaurant kitchen in Canada. We are increasing the load on two panels served by an existing 75KVA transformer by roughly 15KW. The bussing on these panels is large enough to handle the increase so the panels are a non-issue. The calculated proposed connected load on these panels is 135.4KVA (note: the existing pre-renovation load on this transformer may already exceed it's 75KVA nameplate rating).
If we use the NEC (220.56) to calculate the demand load on the feeder to these panels, and then use this calculated demand load to size a new transformer, we would get 93KW (demand factor of 65% of kitchen equipment load + miscellaneous receptacles, etc). Therefore in the U.S. we would replace the existing 75KVA transformer with a new 112.5KVA transformer.
If we use the CEC (8-300(3)) to calculate the demand load on the feeder to these panels, we are obligated to size a new transformer based on the 135.4KVA connected load (100% of connected load). Therefore in Canada, we would replace the existing 75KVA transformer with a new 150KVA transformer.
You can see that there are cost implications here for sizing the new transformers.
I'm pretty sure I'm on the right path with these calculations, just wanted to be certain that I'm not missing something in the CEC that allows us to apply diversity similar to the NEC. Can you all confirm that there are essentially no demand calculations that are applicable in the CEC for a situation such as this?
Thanks for reading and any insight you can provide!
Good call, jdevlin. This is one of the options we are considering.
The only issue with this is that our space's current distribution system is derived from the landlord's electrical service and this service feeds multiple separately metered tenants. With a second transformer, we would have to have two meters for one space, which as far as I'm aware is not a code violation (there are already more than 4 existing taps off of the landlord's service but I believe the existing service main disconnect allows us to get around this - might be a special deviation under CEC 6-104), yet the utility might take issue with it. We also will have to consider the impact of the new transformer on the landlord's service which would be the case with a second 75KVA transformer or a new 150KVA transformer.
The service has a 400A main disconnect switch, assumed to be fused at 400A, which feeds a wireway. Each tenant's feeder has a disconnect switch then a meter tapped off of the wireway. There are 6 disconnects of sizes between 60-100A (and meters) tapped off this wireway.
We have not yet determined if our renovation would impact the existing service. I want to make sure I understand CEC demand load calculations in order to get a clearer picture of what we can and can't apply to the existing service.
The existing feeder to the space is fed by a 100A disconnect (100A fused) at the landlord's wireway. This feeder then extends to another 100A disconnect (100A fused) in the tenant's electrical room. This disconnect then serves another wireway (600V) in the tenant's electrical room. Two 30A disconnects and feeders on this wireway serve roof top units. Another 100A disconnect (90A fused) hangs off of this wireway and serves the existing suspended 75KVA transformer. The transformer does not have secondary overcurrent protection and the panel that it serves is about 1.5 meters away. A second panel is subfed from the first panel.
Clear as mud? I've uploaded a PDF of the single-line if anybody's interested.
Can you get any reduction from 8-106 (3), (4), (5) or (8)?
twh, that depends...
8-106(5) states "Where a feeder supplies loads of a cyclic or similar nature such that the maximum connected load will not be supplied at the same time, the ampacity of the feeder conductors shall be permitted to be based on the maximum load that may be connected at any one time."
So, for instance, can we make the argument to a plans examiner or inspector that in a commercial kitchen only 1 out of 5 coffee brewers would be running at a time? This is assuming that we could argue that a coffee brewer runs in a cyclic manner.
If so, this seems like we can almost cherry pick what loads we will include in our demand calcs. Perhaps I'm just too used to the stringency/specifics of the NEC.