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Old 07-24-2012, 11:50 AM   #1
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Nema 10-30 Trying to better understand poles


Hello,

I am trying to better understand my nema 10-30r. When I look at the break box I see that there is a two pole circuit. The switches have the number 30 on them.

Does that mean it is using two circuits at 15 amp each?

If this is the case, wouldn't this unit not be able to work with appliances requiring 240 volts?

Also, isn't a nema 10-30 suppose to be hot, hot, neutral and as such would need 3 pole? Or is the neutral actually functioning as a ground on this?

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Old 07-24-2012, 01:09 PM   #2
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Nema 10-30 Trying to better understand poles


You have a 240VAC 30A circuit with a neutral. It used to be OK to use the neutral as a ground for special cases but it isn't anymore. You may be grandfathered in your case. If possible you may want to go to NEMA 14-30 instead but this will require 4 wire cable to the panel (2x hot, 1x Neutral, 1x ground). This is a 240VAC circuit due to the two pole breaker and dual hot lines.

The breaker only protects the two hot lines, there is no requirement to put a breaker on neutral and in fact it would be dangerous to do so. That is why no third pole on the breaker. 30A means 30A on each pole not two 15s...

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Old 07-24-2012, 01:22 PM   #3
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Nema 10-30 Trying to better understand poles


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The breaker only protects the two hot lines, there is no requirement to put a breaker on neutral and in fact it would be dangerous to do so. That is why no third pole on the breaker. 30A means 30A on each pole not two 15s...
Okay, so I was going to plug in an appliance that was 240v / 19amp / 4300 watt. Do you see any problem with that?
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Old 07-24-2012, 02:02 PM   #4
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Nema 10-30 Trying to better understand poles


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Okay, so I was going to plug in an appliance that was 240v / 19amp / 4300 watt. Do you see any problem with that?
You really do need a grounding connection. You could wire the neutral terminal on the receptacle to the grounding terminal on the appliance since there is no neutral required and the wire ends up in the same place in the panel, but it's a code violation. If you can replace the receptacle with a grounding one, that would be best.
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Old 07-24-2012, 04:15 PM   #5
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Nema 10-30 Trying to better understand poles


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Originally Posted by mpoulton View Post
You really do need a grounding connection. You could wire the neutral terminal on the receptacle to the grounding terminal on the appliance since there is no neutral required and the wire ends up in the same place in the panel, but it's a code violation. If you can replace the receptacle with a grounding one, that would be best.
If I am using a nema 10-30 plug with a nema 10-30 recepitcal what would be the point of changing the configuration? Is it unsafe or just not standard?
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Old 07-24-2012, 05:13 PM   #6
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Nema 10-30 Trying to better understand poles


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Originally Posted by Sesom

Okay, so I was going to plug in an appliance that was 240v / 19amp / 4300 watt. Do you see any problem with that?
Is it solely a 240vac appliance or is it 240 and120?

I get nervous of sharing neutral and ground even if it was OK way back when. You could argue knob n tube was ok so just leave it? Standards improve, safety is better understood so things change, generally for the better.

If it is a 240v only appliance like a welder then you don't need a neutral anyway so that would be ok..
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Old 07-24-2012, 06:23 PM   #7
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Nema 10-30 Trying to better understand poles


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Is it solely a 240vac appliance or is it 240 and120?

I get nervous of sharing neutral and ground even if it was OK way back when. You could argue knob n tube was ok so just leave it? Standards improve, safety is better understood so things change, generally for the better.

If it is a 240v only appliance like a welder then you don't need a neutral anyway so that would be ok..
It is 240 volt only. It is a flash dryer for screen printing, it does have temperature controls.
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Old 07-24-2012, 06:48 PM   #8
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Nema 10-30 Trying to better understand poles


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Originally Posted by curiousB
You have a 240VAC 30A circuit with a neutral.
aka...a 120/240 circuit

Last edited by jlmran; 07-24-2012 at 06:54 PM.
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Old 07-24-2012, 07:35 PM   #9
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If I am using a nema 10-30 plug with a nema 10-30 recepitcal what would be the point of changing the configuration? Is it unsafe or just not standard?
If you use the neutral terminal for the equipment grounding conductor, then it's not unsafe, just non-standard since the white wire is being used as the equipment grounding conductor. If you leave the neutral terminal unconnected (no equipment ground) then it's unsafe.
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Old 07-24-2012, 08:03 PM   #10
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If you use the neutral terminal for the equipment grounding conductor, then it's not unsafe, just non-standard since the white wire is being used as the equipment grounding conductor. If you leave the neutral terminal unconnected (no equipment ground) then it's unsafe.
Okay so as long as the equipment is wired for hot,hot,ground and the 10-30 receptacle is wired as it regularly would be than it should work correctly?
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Old 07-25-2012, 11:49 AM   #11
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Nema 10-30 Trying to better understand poles


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Okay so as long as the equipment is wired for hot,hot,ground and the 10-30 receptacle is wired as it regularly would be than it should work correctly?
You have to make sure your equipment does not require a neutral. I suspect that your dryer will have the internal transformer to supply any 120Vac it might need so you may not need a neutral.

If you only have 2 hots and a ground coming out of the dryer...then you are good to go with the plug you have. It it has 4 wires....then you need to pull a neut to it and use the recomended plug.
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Old 07-25-2012, 12:14 PM   #12
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Nema 10-30 Trying to better understand poles


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Okay so as long as the equipment is wired for hot,hot,ground and the 10-30 receptacle is wired as it regularly would be than it should work correctly?
Yes, that will work correctly. It's just non-standard and technically a code violation. But it is electrically identical to a proper grounded circuit.

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