Hi all,

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.

WD:
Welcome to ECN forums from one of the 'Jersey Guys'

Kind of an interesting comparison, I'm curious to see haw it pans out.

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!

Not a commercial electrician but it seems to me that adding another 75kva transformer and putting each penal on it's own transformer might be a cheaper/better solution.

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.

WD:
Based on your info above, clarify a few things for all reading this thread please.

Service at the structure (landlord) is 277/480 volt, 3 phase?

Said service has MOCP, and has multiple tenant feeders with meters and mains for each feeder.?

You performed the load calcs on the existing service (landlord), and your calc load for the renovation will not compromise the existing service?

You did not mention the existing feeder to the space, or the OCP on the 75KVA primary and secondary feeders. You did note that there are thoughts of the existing load being an issue.

Can you get any reduction from 8-106 (3), (4), (5) or (8)?

Hotline1, here's what we've got:

Incoming service (landlord) is 600V 3 phase.

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.

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.

Any thoughts?

I would need a letter from an engineer before they would even consider letting me use clause 5, so it isn't like just anyone can cherry pick the loads.

You have an existing kitchen so you should be able to look at their power bills to get the demand for the previous year. (75 kva plus 15 kw is 90 kva, not 112.5 kva) I assume you aren't looking at clause 8 for a reason. Is that reason, because 90 amp overcurrent x 600 volts x 1.732 = 93.5 kw?

Maybe you want to reconsider what "special loads" you are adding to your calculation under 8-210.

Could any of the new equipment be changed to 600 volts to avoid the transformer?

How about adding a new 15 kva xfrmr and a new panel for the new loads?

Sorry, I forgot that you did say the existing transformer might be overloaded.

I'm curious about your calculations. You have a "special load" of 65 kw. I think these loads are usually all on at the same time when the kitchen is operating. The only allowance for motors starting is really that some loads will still cycle. That is a fact on both sides of the border.

The difference must be the basic load. In Canada, you have 70 kw basic. In USA you must have only 47 kw basic. That is 1/3 less and would remove almost all margin for error. I wonder if you have some equipment in the special load category that is covered in the basic load.

Re-reading your earlier post, the term "miscellaneous receptacles" seems out of place.

I should mention that almost every piece of existing equipment in this space is being relocated and therefore a new branch circuit will be required. This is why I am paying so much attention to the existing load and not looking too closely at clause 8-106(8). Summing up the NEC demand loads of all of the existing and new equipment that we are adding gives us 93KW. We know that we are adding roughly 15KW demand load in new equipment alone. So 93KW - 15KW = 78KW in existing demand load which means we are technically overloading the nameplate rating of the 75KVA transformer per NEC calculations. So if we were to use NEC demand for this restaurant, we would consider replacing the existing 75KVA transformer with the next largest standard transformer size - 112.5KVA (or just adding a new 45KVA transformer). Since it appears that CEC requires connected loads to size services and feeders, we would need to size our transformer based on the sum of all of the existing and new equipment - a total that gives us 135.4KW. Therefore I would think we need to replace the existing 75KVA transformer with a 150KVA transformer (or add a second 75KVA transformer.)

We know that a transformer or service upgrade is in our future, the issue is trying to determine if we need a transformer system that can cover the CEC connected load of 135.4KW or a transformer system that can cover the NEC demand load of 93KW.

I don't think there's much we can put ahead of the transformer on the 600V wireway.

twh, I appreciate this dialogue and your insights - it is helping me get a clearer grasp of the CEC.

I understand the issues.

CEC requires that you add "special loads". Can you tell me what loads you think are special?

I would suggest going with the Demand Load of 135.4 KVA, unless there is absolutely no possible way for the Client to exceed 93.0 KVA at any time.

Non-Coincidental Loads may become Coincidental when a Restaurant is packed with Customers.
For example, there may be a time where all Four Coffee Makers are being used for 2-3 Hours, whereas 95% of the time only Two would be used continuously.

A mistake in Design will result in a blown Fuse in the Service Disconnect;
Blown Fuse results in Downtime, Production Loss and Overhead Issues for your Client.
These all equal a Pissed-Off Client; and Pissed-Off Client will result in Penalty Phase for the Designer and Installer.

So, in a vicarious way, a Blown Fuse at the Service Disconnect (Tenant's Main) equals Financial Loss for the Designer-Builder.

I am sorry for not adding any helpful data to this thread.

--Scott (EE)

My take, based upon NEMA transformer sizes and economics...

Go with the nearest standard size -- rounding down.

Because, like the current transformer, NEMA standards are conservative enough to withstand overloads, something around 112.5 kVA should get you by.

IIRC, that's a magic design threshhold, too.

If it's permitted, you might even shop eBay for second hand transformers. I see that Canadian devices sell at a discount all of the time. (600Y120) The next bump after 112.5, IIRC, is 150kVA. Intermediate sizes would be a (very, very, costly) special order.

Thanks all for the input.

As an update, we are applying CEC 8-106(8) which allows us to add proposed connected loads to the peak utility loads. The peak utility load seen by this store in Aug-Sep 2012 was listed as 66.9KW. Doing some math and subtracting the calculated loads of the RTU's on the 600V service, we have determined that the existing 75KVA transformer is only operating at about 39.2KVA. Even with our 15KW load increase, we will not be exceeding its nameplate rating...

If this was a new installation, we would most likely have sized the transformer at 112.5KVA accordingly - summing non-cyclical connected load considerations, as twh recommended, through CEC 8-106(5).