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Author Topic: 3-prong 'dryer' plug  (Read 713 times)

Dave Garoutte

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3-prong 'dryer' plug
« on: August 04, 2017, 10:01:08 pm »

In a venue walk-thru today, I have a choice of a 240v three prong dryer plug or a couple of Edison 120v circuits. 
I am guessing the 240v supply can't be split into two 120v in my distro, which has a 4-prong plug, since there is no common wire.
I have run this PA off of a 20 amp 120 circuit before with no problems.
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Tim McCulloch

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Re: 3-prong 'dryer' plug
« Reply #1 on: August 04, 2017, 10:30:24 pm »

In a venue walk-thru today, I have a choice of a 240v three prong dryer plug or a couple of Edison 120v circuits. 
I am guessing the 240v supply can't be split into two 120v in my distro, which has a 4-prong plug, since there is no common wire.
I have run this PA off of a 20 amp 120 circuit before with no problems.

For sure the 30 Amp plug is missing either a neutral (most likely) or the EGC and you're correct that makes it a no-go.
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Jeff Bankston

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Re: 3-prong 'dryer' plug
« Reply #2 on: August 04, 2017, 11:53:31 pm »

3 prong dryer plug = Hot Hot Ground , no neutral.
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Jonathan Johnson

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Re: 3-prong 'dryer' plug
« Reply #3 on: August 05, 2017, 02:09:06 am »

3 prong dryer plug = Hot Hot Ground , no neutral.

Or hot-hot-neutral with no ground.

Three-prong dryers were wired internally with a bonding jumper between the neutral and the chassis. This is no longer considered acceptable.
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Cailen Waddell

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Re: 3-prong 'dryer' plug
« Reply #4 on: August 05, 2017, 09:45:22 am »

Or hot-hot-neutral with no ground.

Three-prong dryers were wired internally with a bonding jumper between the neutral and the chassis. This is no longer considered acceptable.

Fwiw - not always.  I know of at least one old school dryer without the fancy electronics that didn't need a neutral.  Just two hits and a ground.  There was nothing in it that didn't run on 240v....

But yes - the internal bonding is not acceptable. 


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TJ (Tom) Cornish

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Re: 3-prong 'dryer' plug
« Reply #5 on: August 05, 2017, 10:37:46 am »

In a venue walk-thru today, I have a choice of a 240v three prong dryer plug or a couple of Edison 120v circuits. 
I am guessing the 240v supply can't be split into two 120v in my distro, which has a 4-prong plug, since there is no common wire.
I have run this PA off of a 20 amp 120 circuit before with no problems.
Since your system runs off one 20A circuit that's certainly the easiest route.  That said, it may be possible to use a 3-wire 240v receptacle if it is a H-H-G for devices that can run on 240v power if you spend a few bucks and build an adapter/small OCPD device that contains a 20A 2-pole breaker and adapts to a L6-20R connector.  This could feed a large amp to take some load off the 120v circuits.

Note that the 2017 code requires listed distribution systems so the above may not be acceptable in your area.  Even if it's acceptable for code in your area, it's definitely not acceptable unless you know what you're doing.

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TJ (Tom) Cornish

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Re: 3-prong 'dryer' plug
« Reply #6 on: August 05, 2017, 10:46:48 am »

Or hot-hot-neutral with no ground.

Three-prong dryers were wired internally with a bonding jumper between the neutral and the chassis. This is no longer considered acceptable.
Both H-H-N and H-H-G exist.  The NEMA 10 series is H-H-N and was commonly used for ranges, air conditioners, and dryers.  This is an ungrounded connector and is therefore illegal/deprecated.  The NEMA 6 series is H-H-G and is still in use, though now mostly replaced by the NEMA 14-series which has both a hot and a neutral conductor.

Some older dryers bonded the chassis to neutral, some had external ground lugs where it was presumed you would run a separate ground wire.  120 volt control devices were shunted to the chassis in some cases.

All of those methods are now considered (for good reason) unsafe.
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David Buckley

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Re: 3-prong 'dryer' plug
« Reply #7 on: August 06, 2017, 05:30:19 pm »

The solution to HHG 3 pins is a transformer.  Another 150lbs of kit to lug around :)

But if the PA runs off a single 20A socket, then the "more power" question is only of theoretical interest.  Unless, of course, that socket is one of many on the breaker and there's a bunch of other people's crap plugged in...


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Dave Garoutte

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Re: 3-prong 'dryer' plug
« Reply #8 on: August 08, 2017, 04:21:11 pm »

Thanks, all.
That was my feeling about it.
120v it is!
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