Kiln installation

[Finn12067]

HELP!!!
I hired an electrician to put in a dedicated breaker , wiring and receptacle for 48 amp kiln. The manufacturer specs called for a 60amp breaker to be installed yet he installed a 50amp breaker bc the plug was is a 50 amp plug . The inspector believes this is correct as Well. The manufacturer (l&l) maintains that nec code requires the 60 amp. the kiln 240v/ single phase
I’m caught. Will the 50 amp suffice? Any advice is greatly appreciated .

 

[Little Bill]

I'm allowing this as a code discussion only, please only code related answers.

 

[petersonra]

I'm inclined to agree that a 50 amp plug has to be protected by a 50 amp circuit breaker or fuse.

It seems to me that electric heaters, like an electric kiln, are required to have conductors sized at 125% of actual full load current. I wonder how they managed to do that with a 50-amp plug.

I seem to recall that the maximum size branch circuit for electric heaters is 48 amps by code which may explain the 48 amp rating of the kiln.

 

[James L]

I've wired a couple of kiln receptacles where the specs were about 11.5kw and a nema 6-50 receptacle.

50 amp breaker

 

[rnatalie]

I've had a kiln (ceramics) in my house (it was there when I bought it) and I have helped install kilns for a neighbor who is a glass artist. These things are designed to run for days at a time, so my take is that they are indeed continuous loads and require sizing up the OCD (and hence the wiring) to 125%. Further the "manufacturer's instructions" trump any colloquial interpretations anyhow.

 

[James L]

I've had a kiln (ceramics) in my house (it was there when I bought it) and I have helped install kilns for a neighbor who is a glass artist. These things are designed to run for days at a time, so my take is that they are indeed continuous loads and require sizing up the OCD (and hence the wiring) to 125%. Further the "manufacturer's instructions" trump any colloquial interpretations anyhow.

And the nema 6-50 ?

 

[augie47]

I know nothing about kilns but I can't imagine one being a continuous load (3 hours full load no cycling) but, as noted in Post #5, if the manufacturer ststes a 60 amp breaker is needed, then, IMO, it should be wired with a 60 amp breaker and receptacle.

 

[don_resqcapt19]

... Further the "manufacturer's instructions" trump any colloquial interpretations anyhow.

The manufacturer's instructions cannot change a code rule. The use of a 50 amp receptacle on a 60 amp branch circuit is a violation of 210.21(B)(1).
This should be kicked back to the listing agency as they should not provide a listing for a product where the intended installation is a code violation.

 

[Rock86]

The manufacturer's instructions cannot change a code rule. The use of a 50 amp receptacle on a 60 amp branch circuit is a violation of 210.21(B)(1).
This should be kicked back to the listing agency as they should not provide a listing for a product where the intended installation is a code violation.

210.21(B)(1)... "A single receptacle on an individual branch circuit shall have an ampere rating not less than that of the branch circuit." If the manufacture specified a 60A OCP... that is greater so that would work... no?

Also... a point towards the electrician... 422.11(A) The OCP rating shall not exceed the nameplate... which they didnt do. Also, what does anyone thing about 422.11(F)??

 

[Finn12067]

thanks all for weighing in !!
It would appear from review of the other kiln manufacturers specs for like kilns - it is common practice to use the 50 amp plug and require the 60 amp breaker - so customers caught in the middle - I have reached out to the certifying safety agency to see what they have to say .
Not sure how I reconcile this and get my kiln to work properly . Will a 50 amp breaker work? What is the downside / potential problems with leaving it in ?

 

[Meltric_South]

I'm no expert in kilns, but the plug has to be rated at least to the OCPD as mentioned above by 210.21(B)(1).

Are then any safety issues with the 48A kiln running on a 60A breaker?

Also would the section of the NEC pertaining to this application be 425 Fixed Resistance and Electrode Industrial Process Equipment? The "industrial" is throwing me off.

 

[don_resqcapt19]

210.21(B)(1)... "A single receptacle on an individual branch circuit shall have an ampere rating not less than that of the branch circuit." If the manufacture specified a 60A OCP... that is greater so that would work... no?

Also... a point towards the electrician... 422.11(A) The OCP rating shall not exceed the nameplate... which they didnt do. Also, what does anyone thing about 422.11(F)??

The receptacle must have a rating not less than that of the branch circuit. The rating of the branch circuit is defined as the rating of the branch circuit OCPD.

 

[winnie]

Good for you (OP) reaching out to the listing agency to see what the story is. They may have a reasonable answer for why the manufacturer's instructions violate code. What the electrician did is also _possibly_ a code violation, because you are not supposed to install a 48A _continuous_ load on a 50A breaker. So getting a proper technically supported answer would be useful. Please post back here when you do get an answer.

Know that your kiln with its 48A load on a 50A breaker will most likely work just fine. The kiln might run continuously for hours or days, but once it is up to temperature the thermostat will be turning the heating elements on and off, so the current flow won't be continuous. I don't know what your firing profile is, so don't know the duration of actual continuous operation.

Circuit breakers are designed to be operated at no more than 80% of their trip rating on a continuous basis, so in your installation the circuit breaker itself may run hotter than is desirable and have a reduced life. If this happens the most likely outcome are 'nuisance trips' where what should be a normal load causes the breaker to trip.

-Jon

 

[tom baker]

Yes we would like to see the answer from the manufacturer, and some pictures of what you make.

 

[curt swartz]

I have not worked with many kilns but the ones I have cycle on an off just like a standard oven. The temperature is obviously much higher but the elements still cycle to maintain a set temperature.

 

[Little Bill]

Maybe the 125% x 48A = 60A is for the blower motor part of the kiln?

 

[hbiss]

Kilns don't have blowers.

-Hal

 

[K8MHZ]

Everything I have read indicates kilns are not continuous loads. For example:

How much energy/electricity will I be using?
The simple answer is that firing a kiln costs less than you’d imagine. Even though a kiln draws electricity, it does not draw it continually, so during a typical glass firing, a kiln's elements are drawing power only a fraction of the time. Most digital controllers allow you to enter your cost per kilowatt hour for electricity and they will report back the cost of the firing.
Here’s one formula for calculating the cost of firing your kiln:
1 = Amps
2 = Volts
3 = Estimated Firing time in hours time x .75 (kiln is only on full power intermittently)
4 = Cost per kilowatt hr from your electric bill

Kiln Use Cost & Energy Consumption | Kiln Frog

Kiln Frog guides you through the costs associated with using a kiln, including a handy formula for calculating energy-to-firing costs. Learn more online.

kilnfrog.com

 

[Little Bill]

HELP!!!
I hired an electrician to put in a dedicated breaker , wiring and receptacle for 48 amp kiln. The manufacturer specs called for a 60amp breaker to be installed yet he installed a 50amp breaker bc the plug was is a 50 amp plug . The inspector believes this is correct as Well. The manufacturer (l&l) maintains that nec code requires the 60 amp. the kiln 240v/ single phase
I’m caught. Will the 50 amp suffice? Any advice is greatly appreciated .

I saw on their website that kilns over 48A should be hardwired. Although yours seems to be exactly 48A, according to you, it might be good if you have your electrician install a 60A fused disconnect and direct wire the kiln. Of course you would have to get permission from the mfg to prevent voiding your warranty.

 

[Little Bill]

Kilns don't have blowers.

-Hal

I thought I had seem some with motors/blowers for the venting.