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Range calculations 220.55

Merry Christmas
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cbirschbach71

Member
Location
Wisconsin
Occupation
Electrical contractor
Hey all,

I've been in the trade for 15 years and had my own business for 3. Most of my experience is residential based. I'm trying to do a service calculation for a potential customer. They are going to have 3 kilns. While I know it's not necessary legal, for comparison sake I'm calculating them as ranges. Two are 15.1 KW and one is 9.7 kw. Using note 2, I came up with a final number of 14.6 KW. Here's where I get confused.. for a feeder calculation, do I only use one entry of 14.6 KW for my calculation, or do I need 3? If I'm understanding the purpose of the table, they are assuming that all units will not often be running simultaneously and you can therefore reduce the calculated rating. Any input would be appreciated. I know they are kilns and technically can't be calculated this way, but the times they will be be on are slim to none. Thanks.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
220.55 is specific for cooking equipment and, despite the similarity, can;'t be used for kilns
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
You might do a 220.80 optional load calculation. The demand factor there should help
 
C

cbirschbach71

Member
Location
Wisconsin
Occupation
Electrical contractor
Single phase 120/240. Kilns are 240v. They currently have one 15k and one 10k (60 and 50 amp respectively), but would like the option to add a 3rd. There are no interlocking controls, but if needed I can rig something up. They kinda wanted the option to run all 3 if needed, although I doubt they would all be started at the exact same time
 
E

Elect117

Senior Member
Location
California
Occupation
Engineer E.E. P.E.
I am going to suggest looking into a 120/240 3ph delta service and you can balance the 2 pole loads to put you closer to 200A service with space for office stuff and future.

The kilns would be continuous loads and should be multiplied by 125%.

I have you ~125A on a 3ph panel from just the kilns. Your single phase loads shouldn't push you past 200A.

If you stay with single phase, then you will be at about 300A to 400A board. Depending on what is easier to find.

If they are in a commercial space, they will probably benefit from having a 3ph service rather than upgrading a single phase service.
 
S

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
A kiln is not a range. Ranges have 4 or more surface burners and an oven burner (actually two, which are usually interlocked except maybe when self cleaning). I think a kiln is typically one giant heating element that cycles on and off. I don't believe they cycle much at all as they warm up. Not sure how long warm up takes.

The demand factors in column A or B may work since an oven is more like a kiln, but still not legal. Those columns are limited to appliances up to 8 3/4 KW rating.
 
C

cbirschbach71

Member
Location
Wisconsin
Occupation
Electrical contractor
Thanks for the insight.

I'm not sure three phase would be an option here, and if it is it would be 120/208 wye. Our utility doesn't typically allow a delta service anymore, but I could check. The other wrinkle is this will be a dual occupancy "barndominium". Half of the lower unit will be the wife's pottery shop, with a couple employees and the 2-3 kilns. Other than some basic lighting and receptacles, there isn't much additional load. The upstairs and garage area are going to be the living quarters for them. They were hoping for a "400" amp duplex service with (2) 200 amp disconnects. I'm just not sure 200 is going to be enough for the Pottery shop. They want to stick with separate metering between the business and the living quarters. I just dont think I'm going to have much luck with a 600 amp service and somehow split the metering from the utility, unless we install a private side meter.

I'm a little out of my element on this one, I typically wouldn't pursue a job like this but it's for a good friend and I'm trying to expand my knowledge.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
cbirschbach71 said:
The other wrinkle is this will be a dual occupancy "barndominium". Half of the lower unit will be the wife's pottery shop, with a couple employees and the 2-3 kilns.
Click to expand...
I say your kiln load is 167Amps I don't think its 'continuous' per the NEC definition as they cycle on and off with a controller or infinite switch, as for your service design I'd suggest going for a 225A loadcenter or a commercial 250A - 400A panelboard for the 'pottery shop' panel.
 
C

cbirschbach71

Member
Location
Wisconsin
Occupation
Electrical contractor
tortuga said:
I say your kiln load is 167Amps I don't think its 'continuous' per the NEC definition as they cycle on and off with a controller or infinite switch, as for your service design I'd suggest going for a 225A loadcenter or a commercial 250A - 400A panelboard for the 'pottery shop' panel.
Click to expand...
Yeah I think if they want the ability to run all three kilns it's going to require a 600 amp service, 400 for the Pottery shop and 200 for the residential portion. I think if they only wanted two kilns a 200 amp service would handle it.
 
E

Elect117

Senior Member
Location
California
Occupation
Engineer E.E. P.E.
It won't be enough for the pottery studio.

I would suggest a minimum of 300A commercial space if not more. You should take whatever other equipment they plan to use into account as well. Like throw wheels, water heaters, extruders, etc.

I would very much make sure the utility does not offer a 120/240V 3ph delta service. It would be perfect for your application.
 
Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
Unless it's a closed delta, you only have two usable 240v sources (each real transformer), so that doesn't make sense over a 208/120 wye service. Yes, the kilns will take longer to heat and won't get quite as hot, but the manufacturer can give the specifics. Or you add boost transformers. Or get a big single phase service.
 
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Elect117

Senior Member
Location
California
Occupation
Engineer E.E. P.E.
The open delta can be used if it is sized appropriately.

You are going to see the line currents at the service which will look like all three phases. It is less efficient means of supplying power and I don't think it is a cost effective solution for the utility. I just wanted to clear that up because some people think that the open phase on the open delta isn't useable, when it is.

www.electricalpereview.com

Open Delta Transformer Connection - Electrical PE Review

Let's calculate the following: The maximum power of an open delta transformer connection, the new line voltages of the open delta transformer, the new line currents of the open delta transformer, the new phase currents of the open delta transformer, and draw all phasor diagrams for the open delta.
www.electricalpereview.com www.electricalpereview.com
 
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