ECN Forum Forums Code Related Discussion Canadian Electrical Code Topics Canadian Demand Factors

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).