Skutt KS-1027 section removal

[neilestrick]

1 hour ago, marymae said:

So really, making this kiln a 1018 isn't saving much in amps compared to the 1027.  True? 

True. If the kiln pulls 48 amps and you take away one section, or 1/3 of the elements (we'll assume all the elements are the same), then you'd have a kiln that pulls 32 amps. However the 32 amps isn't enough power. The issues is that there's a lot of heat loss out the lid and the floor, and the 4 elements don't have the power to deal with that like the 6 elements did. So we have to increase the power of the 4 elements to make up for it. So you end up with a 40 amp kiln with 2 sections, and a 48 amp kiln with 3 sections. The only way to really save power is to go to a smaller kiln.

[Dick White]

4 hours ago, neilestrick said:

I've spoken to L&L about this before, because I occasionally run into an electrician who will not use the 50 amp cord on a 60 amp circuit. L&L said this is sort of a gray area, and all the 48 amp kilns get UL listing with the 50 amp cord because the cord uses 6 gauge wire and can handle the 60 amps should it need to. If you look at the smaller kilns made by L&L and Skutt that pull 20 amps, they size the power cord for the 30 amp breaker, not the 20 amp draw. 

So, what we are saying here is that the weak point in the circuit is the breaker which can only handle 80% rated capacity if fully loaded for more than 3 hours. Thus, a 60 amp breaker for a 48 amp continuous load. The wiring in the rest of the circuit is all 6 ga (or better) to match the 60 amp breaker, including the kiln power cord, even though only 48 amps will pass. The only exception is the inch and a half or so of the prongs of the 6-50 plug and receptacle. Are they truly limited in their capacity to pass no more than 50 nominal amps, or is the plug and receptacle more about the NEMA configuration to prevent end-user mix and match stupidity?

[Bill Kielb]

9 hours ago, Dick White said:

So, what we are saying here is that the weak point in the circuit is the breaker which can only handle 80% rated capacity if fully loaded for more than 3 hours

I think the simple answer is the breaker is sized per code which treats continuous loads differently than non continuous because of the potential for extra heating produced in the breaker. Most breakers under NEC are designed for max loading of 80% for the same reason. The cords are sized and derated appropriately for corded conductors that also produce more heat because they are molded into a cord. The next size up rule often influences the materials to build things and stay safely conservative.

Electricians in the states should be used to using 80% breakers, yet often when it comes to kilns they want to put a 30 amp breaker on a 30 amp kiln. Go figure, you would think they would be looking not to exceed  80% of the value of the breaker they just purchased or 37.5 amps. (125% of 30 amps btw)  Is it a weak point? I view it as a design criteria. In North America breakers are generally produced and sized at 80% for continuous loads but will trip at there published amperage. The sizing is very much about the heat produced and the life and safety of the breaker. 100% breakers can be purchased, they need to meet very stringent testing standards before they are designated 100%.and usually have to be enclosed in a minimum size enclosure for cooling.

There are many skilled electricians who deal with this daily, still there are probably many more line electricians that likely don’t so for kilns it is often a challenge.

So virtually any retail breaker one buys for the home is an 80% breaker meaning it was designed to be loaded at 80% capacity for a continuous load.

Edited February 23, 2023 by Bill Kielb

[neilestrick]

19 hours ago, Dick White said:

The only exception is the inch and a half or so of the prongs of the 6-50 plug and receptacle. Are they truly limited in their capacity to pass no more than 50 nominal amps, or is the plug and receptacle more about the NEMA configuration to prevent end-user mix and match stupidity?

This is the big question, and one I haven't been able to find an answer to. 15 amp outlets have the same internal parts as 20 amp outlets, but that may or may not be true for the larger stuff. A lot of the 30 amp replacement plugs are sold as a 30/50 amp plug depending on how you put them together, so in that case I think it may be true that it's just a configuration issue. But I cannot find anything that says what amperage would actually melt a 50 amp outlet. I found a few electrical forums where folks said it would likely take at least 50-60 amps to melt a 30, and someone said about 100 to melt a 50, but that's all just opinion. I also found electricians who said that it doesn't matter what UL says, it can't be hooked up to a 60 amp breaker with that cord because it violates code, and others who said it absolutely matters what UL says because they wouldn't list that setup if it did violate code.

In most cases an inspector will defer to the manufacturer's recommendations, which in this case are that it has to be on a 60 amp breaker, and it can be done with the 50 amp cord. I am of the opinion that the manufacturer's wouldn't be doing it that way if it was a safety issue, because that would put an awful lot of liability on them. And honestly, there would have been houses catching fire from that setup for the last 75 years if it wasn't safe.

[Hulk]

My Dad pointed out that the "knob and tube" wiring of old did have an advantage over the Romex of today - it dissipates heat better when overloaded.
That wiring shouldn't be overloaded to the point where dissipating heat is an issue, should go without saying*.

The charger that came with our Volt failed earlier this week, likely a combination of several years of daily handling (wind it up, unwind, repeat) and closing the cable in the door, oops.
Any road, the cable from the transformer box to the plug definitely warmed.
Needing (packed away) tools to diagnose & repair, we ordered a replacement; its cable is heavier, it is not getting warm.

*said it anyway.

[Bill Kielb]

1 hour ago, neilestrick said:

t. I found a few electrical forums where folks said it would likely take at least 50-60 amps to melt a 30, and someone said about 100 to melt a 50, but that's all just opinion.

I agree, if they talk about SCCR Short circuit current ratings then they have a better understanding how things are ultimately rated. If the manufactures design has been certified, then their engineering has established it. It’s a 48 amp load so a 50 amp cord seems perfectly logical and the default short circuit current rating of the cord / plug is likely very much higher than 50 or even 60 amps at 240 volts dead short.

UL 508A table SB 4.1 for power outlets is partially what you are looking for, except the ratings are in ka or thousands of amps over a time period.

It’s far more complicated to get everything approved and to work safely so the engineering and certifications are the best values. 

some fun reading page 14:  https://www.overcurrentprotection.org/wp-content/uploads/2021/08/Review-of-SCCR-and-NEC-2020-Presentation.pdf

Still sometimes folks just have their own idea.
I have been waiting for two months for a part time electrical inspector of one of our local villages to allow tandem breakers in the panel I have shown above. I was trying to add 1 circuit actually.I finally said the delay is getting so costly I will just change all the panels to newer with more positions. Approve the drawings already! 20 new 100 amp panels, drywall retrofit, labor, lots of extra money paid ……. By the end user.

Edited February 24, 2023 by Bill Kielb

[Bill Kielb]

1 hour ago, Hulk said:

My Dad pointed out that the "knob and tube" wiring of old did have an advantage over the Romex of today - it dissipates heat better when overloaded.

While true, the thermal rating of the wire cloth covering was rated considerably less than todays thermoplastic covered wiring. Also probably helped make ungrounded circuits acceptable or the norm in a way. Not much good about it other than it could be cooled in free air but also free to start a fire under fault. 

[Hulk]

When coated at all, the knob and tube of old I've seen had a loose sleeve of woven white fiber -asbestos - which thermally rates rather well would be my guess, else bare copper between the knobs.

Google images of wire coated with blackened/tarred material may have been ubiquitous, I just haven't seen it in person.
No doubt three wire Romex, when properly sized and protected by its breaker, is superior in every way.

[neilestrick]

I also found a lot of discussions about this exact same issue happening with home charging stations for electric cars. Apparently they have a 14-50 outlet (50 amps), but to be able to charge at their peak power of 48 amps they have to be on a 60 amp breaker since they're continuous draw like kilns.

[Bill Kielb]

7 hours ago, Hulk said:

When coated at all, the knob and tube of old I've seen had a loose sleeve of woven white fiber -asbestos - which thermally rates rather well would be my guess, else bare copper between the knobs.

 

Have only seen remaining in a handful of old houses — all fabric and rubber covered and interestingly only left in the attic and not replaced. Asbestos was used for a bit with the fabric covering for sure. Another great feature. Growing up, I think I remember seeing a can of this or two. Heck when I was eighteen I can remember tearing off a big piece of asbestos paper to protect against welding splatter.

 

Edited February 24, 2023 by Bill Kielb