NEMA 6-50R Plug Conversion

[packrat31]

Hi, I have a NEMA 14-30P wall outlet, but the kiln I just bought is a NEMA 6-50R plug. 

What do I do? I was going to get my electrician to switch the plugs, but came across these adapters. Are they safe to use?

[Mark C.]

what is your kiln amp draw? 30 amps or 50 amps?????

This is needed to figure this out

what matters will be the wire size  to that outlet as well as the adapator wire size-

do you know any of those things as well?

wire size is critical 

[Mark C.]

Researching thoise outlets and plugs -your NEMA 14-30P wall outlet is rated for 30 amps (#10 wire size)-most likely on a 30 amp bcurcuit breaker

Your kiln has a NEMA 6-50R plug which is for 50 amps and needs a #6 wire and at least a 50 amp curcuit breaker if not a 60 amp breaker (25% over for safety) 

On just this info that adaptor is not safe and do not use it as its afire hazard.

My guess is you need a new #6 wire and new outlet for this new kiln.

what is the amp draw on the plate say on side of kiln?

[packrat31]

Thank you so much for the quick and thorough responses! I will ask my electrician what the breaker can take - but you're right... I see the 14-30R is 30 AMP!

Here are the details from both my outlet plate and kiln plate.

 

My kiln plate says:

AMPS 45
Watts 10800
240V

 

My wall outlet says:

NEMA 14-30R
30A
126/250V

[neilestrick]

5 minutes ago, packrat31 said:

My kiln plate says:

AMPS 45
Watts 10800
240V

Kilns must be on a breaker that is rated 25% greater than the draw of the kiln, but not more than 50% greater, so your kiln should be on a 60 amp breaker, and use the 50 amp plug that is currently on it. Your 30 amp outlet is likely on a 30 amp circuit. You'll need to pull new wire (at least 6 gauge), and change the outlet and breaker. Talk to your electrician. Do not let them put it on a 50 amp breaker, as that will not be up to code.

[packrat31]

I have another kiln that has a NEMA 14-30 plug, and when looking at it again the kiln face plate says AMPS 48/1. I've plugged it in before and wasn't getting any power to any of the coils but the top row (even after replacing broken coils and both relays). The electrician looked it over and was stumped. Could this 30AMP discrepancy between breaker(30) and kiln requirements(60) be the cause?

Thank you all for your input. I thought I'd done all my research, but still learning!

[Bill Kielb]

52 minutes ago, packrat31 said:

have another kiln that has a NEMA 14-30 plug, and when looking at it again the kiln face plate says AMPS 48/1

There is really no way that plug ought to be on that kiln. Your electrician should be able to wire correctly and safely so I would not trust the previous folks that wired that plug to it.. Not all electricians are savvy with kilns though, it’s not their mainstay, but when presented with such disparity they should realize the basic safety and code issues at hand. It sounds like you will need a kiln tech or at least someone who can confirm from the wiring diagram through the basic electrical and code requirements.

[Dick White]

A 14-30 plug/receptacle is really just two adjacent, but independent, 120V circuits from the panel so that they are on different phases of the incoming service. That way, certain positions of the switch can draw from both circuits simultaneously to get 240V. Other positions of the switch are drawing only 120V for which the neutral is required. That's why there are four prongs on that plug - two 120V hots, the neutral, and the safety ground. A 6-50 plug/receptacle is a full 240V circuit always drawing from both sides of the panel, and there is no neutral, thus only 3 prongs are needed on the plug. They cannot be mixed as one needs the neutral and the other doesn't have a neutral.  You need to study the wiring diagram of the old kiln to determine how it uses and combines the voltages. Some old kilns were simply separate 120V kilns stacked on top of each other to create a similar amount of heat as a 240V kiln. Other old manual kilns with High/Med/Low switches used 120V on low and 240V on med. and high. Both these configurations require the neutral. Newer 240V kilns use only the two hot legs throughout the whole kiln. If you don't have a manual with the wiring diagram for your old kiln, tell us the brand and model and we can probably find a wiring diagram.

The above does not address the amperage issues. As already noted by others, running a 45 or 48 amp kiln on a 30 amp circuit is an open invitation for the fire department to pay a visit. Get the circuit fixed first with a 60 amp breaker and wire size to match (this is needed to accommodate the 125% requirement in the code for kilns). Then we can sort out the plugs. If it turns out the old kiln is in fact a 120/240V device needing a 14-50 plug and receptacle with neutral, it is possible to put a 14-50 plug on the new kiln cord and just not use the neutral prong. That way you can use the same receptacle for either kiln. Or, maybe, the 14-30 receptacle is left over from an old dryer circuit, but you need to replace that whole circuit anyway before you can use it for a kiln.  And because the older kiln draws 48 amps, the 14-30 plug on it is wrong right from the get-go. Or possibly the older kiln is a true 240V kiln and should have a 6-50 plug, same as the new kiln, but you need to replace that plug anyway. The kiln wiring diagram will inform us what is needed.

As for why the top coils in the old kiln did not heat, that sounds like a wiring fault that needs to be traced. Again, the specific wiring diagram for that kiln is needed.

So, to summarize, tell us the exact brand and model of the kilns and we can help you find the wiring diagrams. Then you can work with the electrician to get it all working.
 

[packrat31]

Wow! Thank you so much, that was really helpful - especially re: 120V/240V with the neutral.

This secondary kiln with the questionable 14-30 plug is an Euclids. I just emailed them to hopefully get my hands on a wiring diagram or manual. It has two faceplates on the kiln computer box that are confusing as to what AMP it needs.

Faceplate #1:

CRT 180AF
#1294-95
AMP 30
PH/HZ 3/60
KW 10

I started questioning what AMP it needed when I saw this additional faceplate/sticker by the manufacturer on the computer also:

Replacement Elements
CRT 180
208V
AMP 48/1

[Bill Kielb]

1 hour ago, packrat31 said:

Replacement Elements
CRT 180
208V
AMP 48/1

Yes, 208 v elements says get this straightened out. 208 v elements  will draw significantly more amperage at 240v. Definitely get the diagram and you will need to check several things including if the original elements are still in there. Likely some work to make this fit your situation but doable.

[PeterH]

Just sharing my confusion about US power supplies.

All NEMA 14 devices offer two hots, a neutral, and a ground, allowing for both 120 and 240 V when supplied by split-phase power, or 120 and 208 V if the supply is three-phase.

Might we be talking about a 208v 3-phase kiln?

 

4 hours ago, packrat31 said:

CRT 180AF
#1294-95
AMP 30
PH/HZ 3/60
KW 10

3-phase  would imply 3 208v elements each generating 10000/3 watts.

For each element i=W/V = 10000/3/208 = 16A per phase. So 48A in total.

4 hours ago, packrat31 said:

Replacement Elements
CRT 180
208V
AMP 48/1

 

 

[Bill Kielb]

49 minutes ago, PeterH said:

Might we be talking about a 208v 3-phase kiln?

I am thinking not as the kiln is marked 48/1 which usually means 48 amps single phase. But your theory would be a reason why a 30 amp plug was used and …….. why now when it’s plugged in to a single phase source not all the elements work. All the more reason to sort out  how it was actually wired in the past and will the OP need to change the elements to 240v and wire as single phase. Something I would expect an electrician to determine first and foremost, but kilns and electricians not necessarily a good mix.

[PeterH]

1 hour ago, Bill Kielb said:

I am thinking not as the kiln is marked 48/1 which usually means 48 amps single phase. But your theory would be a reason why a 30 amp plug was used and …….. why now when it’s plugged in to a single phase source not all the elements work. All the more reason to sort out  how it was actually wired in the past and will the OP need to change the elements to 240v and wire as single phase. Something I would expect an electrician to determine first and foremost, but kilns and electricians not necessarily a good mix.

My thinking was that the 48/1 -- on the plate about replacement elements -- was consistent with  3 x 208V elements which -- if wired in parallel -- would be a 48A single-phase load giving 10KW.

On the other hand  I read the main plate as saying 3-phase (PH/HZ 3/60).

If the plug was factory-installed it is highly likely to be within code (in some context).

My knowledge of 3-phase practice only goes as far as knowing √3 is a magic number, and 16*√3 = 27.7

[Bill Kielb]

40 minutes ago, PeterH said:

My thinking was that the 48/1 -- on the plate about replacement elements -- was consistent with  3 x 208V elements which -- if wired in parallel -- would be a 48A single-phase load giving 10KW.

 

Yes, good catch, this kiln was built for 3 phase operation so the plug and wire size are fine for that operation. Needs to be re elemented and rewired to operate at 240v

[PeterH]

2 hours ago, Bill Kielb said:

Yes, good catch, this kiln was built for 3 phase operation so the plug and wire size are fine for that operation. Needs to be re elemented and rewired to operate at 240v

So is it likely that both the new and the (rewired) old kiln could share an (installed to code)  NEMA 6-50R socket?

... really what should be considered/needed for house re-wiring for both kilns, if the rewired one will be 10KW at 240V  (~42A). [To be confirmed when more details emerge.]

[Bill Kielb]

56 minutes ago, PeterH said:

2 hours ago, Bill Kielb said:

 

So is it likely that both the new and the (rewired) old kiln could share an (installed to code)  NEMA 6-50R socket?

Yes, North America codes are pretty similar so in the end at 240v  assuming 10k+ wattage, will likely be fine on 50 amp outlet and likely 60 amp breaker. The rule here protects the breaker from overheating under continuous load, hence the 25% over rating which is actually consistent (reciprocal) of the never load a breaker greater than 80% of its rating rule. 

The US has split phase 240v, so a bit odd with respect to the rest of the world but most of our household loads are 120v. It’s the old higher amperage vs higher potential safety argument. Split phase in general is more expense, wire etc….

Either way, she will need to rewire both and if they are nearly identical in wattage then  sequentially share a code compliant branch circuit. If concurrent ops are needed, then another branch, another receptacle …..

Good catch though, may explain a lot.

[packrat31]

You guys hit the nail on the head with figuring this out - thank you! This thread has been unbelievably helpful. I'm still absorbing all this new knowledge and planning what to do next this these kilns. Having them both on the 6-50R would be great if I'm switching one already.

Side note: The plug looks like it could have been a DIY job from the past owner.

I also just got a message back/wiring diagrams from Euclids Kiln, if you're interested to see.

Based on the spec plate the kiln was 208V 3 phase that you now likely have hooked up on 240v 1 phase.
This will require new elements for 240V, wiring for single phase, as well as being fused on a 50 amp breaker.
I have attached the old diagram from 1996.

 

CRT180AF diagram.pdf

[Mark C.]

As I mentioned new wire to plug (#6) and new plug

That 208V kiln needs new single phase elements as you mentioned as well.

Forget plug adaptors

 

[packrat31]

Absolutely - the plug adaptors are out the window.

[Bill Kielb]

2 hours ago, packrat31 said:

and planning what to do next this these kilns.

It looks like he gave you the wiring diagram for the 240v single phase retrofit. Are you good with it or have someone who can do the work? Interesting in the diagram, T1 is the only switched lead, T2 is always hot. They likely don’t let them build it this way anymore.

[neilestrick]

1 hour ago, Bill Kielb said:

Interesting in the diagram, T1 is the only switched lead, T2 is always hot. They likely don’t let them build it this way anymore.

Correct me if I'm wrong, but with it wired that way, if you come into contact with an element while the kiln is plugged in you're going to get a shock.

[Bill Kielb]

23 minutes ago, neilestrick said:

if you come into contact with an element while the kiln is plugged in you're going to get a shock.

Yep. Looks like an early non standard design. I should correct that, single phase 240, you could make T2 the neutral (Not USA 240) so this actually would be fine. Just label L2 Nuetral.   Further correction, L2 is fused for the control transformer so it needs work to make safe.

[neilestrick]

1 hour ago, Bill Kielb said:

Yep. Looks like an early non standard design. I should correct that, single phase 240, you could make T2 the neutral (Not USA 240) so this actually would be fine. Just label L2 Nuetral.   Further correction, L2 is fused for the control transformer so it needs work to make safe.

I think there are 3 options:

1. Put in one more relay, same type as the existing ones. Both legs of 1 and 6 come off of one, both legs of 2 & 3 come off of one, both legs of 4 & 5 come off of one. T1 and T2 both feed the relays. Those relays should be standard 25 or 30 amp kiln relays.

2. Run T2 through a 50amp relay that's wired to the Safety output on the controller. You'd also need a small relay to act as a pilot for the 50 amp relay. There may not be room for all that in there, and running the big wires through it can be a hassle in a tight space.

3. Wire it as shown, but have a disconnect on the wall so you can easily kill the power whenever you load and unload the kiln.

[Bill Kielb]

15 hours ago, neilestrick said:

think there are 3 options:

I think a redesign is in order for sure. All those solutions above work BTW. I think I would go with three control relays and break both phases as typical across each relay, works in any country in the future.. Preferable distribution would be top, middle, bottom so three zone control would be possible. Would need to know resistance or wattage of the elements though. As far as a safety contactor It’s an easy add if desired. I have a very economical source for 24 vac 60 amp  rated resistive  dp contactors, they are common in HVAC? In  any event, the existing voltage, and phasing must be determined as well as the element resistance in order for a decent design to  be created. 
 

one thing for sure, I would label everything permanently when done. Decent planning up front makes this project very doable.

[neilestrick]

17 hours ago, Bill Kielb said:

Preferable distribution would be top, middle, bottom so three zone control would be possible.

Ideally, yes, but with the way the elements are wired in series that's not really possible. I wonder if they have a different element configuration on newer models that could be used.