50A Receptacle on 60A Circuit ??

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busman

busman

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Location
Northern Virginia
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Master Electrician / Electrical Engineer
Instructions for a kiln quote load at 48A. Comes with 6-50P (50A plug). Requires 60A Fuse. As far as I can see, this violates 210.21(B)(1). I e-mailed the manufacturer and this is what I got back:

"The use of a 50 amp plug on kilns with a 60 amp circuit is a widespread and long standing practice that has been approved by UL."

What am I missing? I'm guessing that UL approved a 50A plug on a 48A load by assuming is was NOT continuous, but that's just a guess. Anyone else run into this? I just don't get how I can put a 50A receptacle on a 60A circuit and meet the code requirements.

Thanks and Happy Holidays,

Mark
 
if you could find the holy grail of having 50a receptacles and 6/4 cable on 60a breakers, you will be the hero of temporary power guys everywhere
 
busman said:
Instructions for a kiln quote load at 48A. Comes with 6-50P (50A plug). Requires 60A Fuse. As far as I can see, this violates 210.21(B)(1). I e-mailed the manufacturer and this is what I got back:

"The use of a 50 amp plug on kilns with a 60 amp circuit is a widespread and long standing practice that has been approved by UL."

What am I missing? I'm guessing that UL approved a 50A plug on a 48A load by assuming is was NOT continuous, but that's just a guess. Anyone else run into this? I just don't get how I can put a 50A receptacle on a 60A circuit and meet the code requirements.

Thanks and Happy Holidays,

Mark
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I was thinking maybe they had a 50A breaker in the kiln, but that still would not deal with the apparent violation. i wonder why UL would deliberately approve such a thing. maybe an email to UL is in order. if nothing else just out of curiosity.

can you change the 60A cb to a 50A?
 
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Just because UL approved the 50 amp male cord connector does not change the code and let you put the 50 amp receptacle on a 60 amp circuit. As them to provide you with a letter from UL directing you to make the installation in violation of the NEC rules.
 
Thanks for all the replies. I'm doing this installation tomorrow. I didn't want to go toe-to-toe with the kiln guys unless I was sure I was right about the NEC. I think I'll install the 50A rcpt. on a 50A breaker and see what happens. I'll also inquire whether the kiln runs for 3 Hrs. continuous.

Thanks for the help.

Mark
 
Pottery kilns run for well over 3 hours. But I think they are like any other oven -- once heated up, the element cycles on and off. So it should not be a continuous load.
 
For a manufacturer to state that "UL Approved" anything would raise a flag to me. UL does not approve, but lists and labels equipment. I would take a closer look at the equipment label and see if there is an actual UL identification on the label.

Something here seems wrong, and I would be concerned. A call to UL is an easy way to determine if the equipment is listed, although it may be listed by a different NRTL.
 
suemarkp said:
Pottery kilns run for well over 3 hours. But I think they are like any other oven -- once heated up, the element cycles on and off. So it should not be a continuous load.
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Indeed. We do some work for a glass artist who uses electric kilns. The temperature must be precisely controlled for the pieces to set and temper correctly. We use some heavy duty mercury contactors which cycle the element on and off.
 
From the website, it looks like this is a continuous load. The plot thickens.

[FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular,Trebuchet MS]Energy, Time and Firing Costs: This hasn't been tested on the e23T-3 but on an e23T (with 2-1/2" brick) typical heat up to cone 6 with a 85 pound load and with Vent-Sure on at 240 Volt/single phase is 6-1/2 hours, 58 kW hours, $5.80 @ 10 cents per kW hour.[/FONT]

​
Mark
 
busman said:
From the website, it looks like this is a continuous load. The plot thickens.
[FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular,Trebuchet MS]Energy, Time and Firing Costs: This hasn't been tested on the e23T-3 but on an e23T (with 2-1/2" brick) typical heat up to cone 6 with a 85 pound load and with Vent-Sure on at 240 Volt/single phase is 6-1/2 hours, 58 kW hours, $5.80 @ 10 cents per kW hour.[/FONT]

​
Mark
Click to expand...

I'll still bet lunch the elements cycle on and off. I could turn the oven on in my kitchen at 10 am for a 6 pm dinner and cook an entree, bread/rolls, casseroles, a cake/pie, etc. and it cycles on and off as well.
 
Mark, if the kiln is listed by a NRTL and the manufacturer's instructions specifically tell you to install it that way, I would say that 110.3(B) would apply since the manufacturer's instructions are part of the listing procedure. :smile:

Take a look at some hair dryers that exceed the rating of the circuits, they meet the listing requirements.
 
charlie said:
I would say that 110.3(B) would apply since the manufacturer's instructions are part of the listing procedure.
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How do we know that those instructions are in fact part of the listing?

The words in 110.3(B) seem to indicate that only instructions included in the listing or labeling are to be followed.

In other words, not any instruction the manufacturers decided to include, only the instructions included with the listing.

I might buy a dishwasher that says 'only use brand X soap'. If I use brand Y soap is that a 110.3(B) violation?
 
charlie said:
Mark, if the kiln is listed by a NRTL and the manufacturer's instructions specifically tell you to install it that way, I would say that 110.3(B) would apply since the manufacturer's instructions are part of the listing procedure. :smile:

Take a look at some hair dryers that exceed the rating of the circuits, they meet the listing requirements.
Click to expand...
The listing and 110.3(B) cannot change the code rules. No matter what the listing and instructions say, you can't put the 50 amp receptacle on the 60 amp circuit.
 
charlie said:
Mark, if the kiln is listed by a NRTL and the manufacturer's instructions specifically tell you to install it that way, I would say that 110.3(B) would apply since the manufacturer's instructions are part of the listing procedure. :smile:

Take a look at some hair dryers that exceed the rating of the circuits, they meet the listing requirements.
Click to expand...

So it would not be a violation if the kiln is plugged into the 60a circuit , but if it is not plugged in the receptacle is a violation ? :-?
 
I think they have got a kiln that cannot be plugged into a NEC compliant circuit.

Thanks for all the help. I plan to contact UL on Monday.

Mark
 
I'll take that bet ,..let's say some mod privileges and if I lose ,..hmmm... errr,....... well I'm not gonna,.. so it don't matter:smile:
 
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