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Author Topic: 3 Phase Single Phase Question gig problem  (Read 2389 times)

Dave Barker

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3 Phase Single Phase Question gig problem
« on: April 20, 2015, 09:32:51 am »

So I was helping on gig this weekend.  Not my rig, not my equipment, not my gerry rigged connector, don't crucify me. Hotel ballroom with single phase 240 connection.  Company has 3 phase distro and had a "california" plug that doubled up 2 legs to a single leg to get the feed from the single phase plug.  So one leg of the single phase was actually feeding 2 legs of the 3 phase distro.  When we metered the single phase we had 120 per leg everything looked great.  When we plugged into the distro voltage dropped to 96 volts and had 30 some volts from one of the legs to ground.  Guy that owns the rig says they connect up this way all the time with no issues before but we certainly had issues that day. 

We removed the distro and I ran to my shop and got another single phase distro and did everything correctly.

My question is what would be causing the voltage issues just to know for future.

Thanks
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Mike Sokol

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Re: 3 Phase Single Phase Question gig problem
« Reply #1 on: April 20, 2015, 10:08:51 am »

So I was helping on gig this weekend.  Not my rig, not my equipment, not my gerry rigged connector, don't crucify me. Hotel ballroom with single phase 240 connection. 

What connector did the Hotel ballroom have for single-phase 240-volts? Was that the Cali-50 or was it a NEMA 14-50 Stove plug which you adapted to the Cali-50? When you measured the 96 volts, were you testing between the hot leg and the neutral, or the hot leg and the ground? Did you happen to measure the opposite leg voltage at that time? If you did I suspect it whould have raised by 20 volts or so to around 140 volts. Something is very fishy with the neutral and ground here, and it ain't the old tuna sandwich sitting in the distro rack.  ::)
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Dave Barker

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Re: 3 Phase Single Phase Question gig problem
« Reply #2 on: April 20, 2015, 01:52:09 pm »

It was a NEMA 14-50 Stove plug in the wall of the hotel to the cali 50 plug.  When I measured out of the wall with nothing connected everything was fine.  Inside the cali 50 plug was the wiring that combined the black/red of the hots going to the 3 phase distro.  The Blue lead was the other side.  There was neutral and ground. 

The 97 volts was measured coming out of the edison outlets on the distro between hot and neutral and it read this on all 3 phases of the outlets.  Trying to remember, when I measured from neutral to ground I thought I had somewhere in the 30 volt range this was on the outlets of the distro again.

We have used this distro many times before so I don't feel anything "inside" the distro is a problem.  Certainly when connected to 3 phase power we have no issues.

When I brought in my single phase box connected up/removed the cali connector everything measured perfect.
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TJ (Tom) Cornish

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Re: 3 Phase Single Phase Question gig problem
« Reply #3 on: April 20, 2015, 02:06:49 pm »

It was a NEMA 14-50 Stove plug in the wall of the hotel to the cali 50 plug.  When I measured out of the wall with nothing connected everything was fine.  Inside the cali 50 plug was the wiring that combined the black/red of the hots going to the 3 phase distro.  The Blue lead was the other side.  There was neutral and ground. 

The 97 volts was measured coming out of the edison outlets on the distro between hot and neutral and it read this on all 3 phases of the outlets.  Trying to remember, when I measured from neutral to ground I thought I had somewhere in the 30 volt range this was on the outlets of the distro again.

We have used this distro many times before so I don't feel anything "inside" the distro is a problem.  Certainly when connected to 3 phase power we have no issues.

When I brought in my single phase box connected up/removed the cali connector everything measured perfect.
The only way to get 97 volts on all three phases is if the neutral is completely broken somewhere, and the meter is reading induced voltage.  Using this would have been extremely dangerous and would have blown up gear. 

Using a space heater, high wattage PAR can, or a Wiggy to do a load test on all phases is the only way to truly be confident that your power distribution is solid.
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Mark Cadwallader

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Re: 3 Phase Single Phase Question gig problem
« Reply #4 on: April 20, 2015, 04:07:03 pm »

NEMA 14-50 leg A @ 0 degrees; leg B at 180 degrees; neutral; ground.

Cali to distro: leg X at 0 deg (A); leg Y at 0 deg (A); leg Z at 180 deg
(B);  neutral; hot.

Is that the hook-up? Mark C.
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Mike Sokol

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Re: 3 Phase Single Phase Question gig problem
« Reply #5 on: April 20, 2015, 04:25:39 pm »

NEMA 14-50 leg A @ 0 degrees; leg B at 180 degrees; neutral; ground.

Cali to distro: leg X at 0 deg (A); leg Y at 0 deg (A); leg Z at 180 deg
(B);  neutral; hot.

Is that the hook-up? Mark C.

I'll bet this was a NEMA 14-50 connected to two legs of a 3-phase 208/120 WYE transformer. If so, that's a 120 degree phase shift , and it should measure 120 volts from line to neutral, and only 208 volts leg-to-leg, instead of the expected 240-volts if this was actually a 180-degree split-phase 120/240-volt system. Is 240 minus 208 where the lost 32 volts is being measured? I don't know how you metered it, but that's 32 volts less than expected, sorta... ???
« Last Edit: April 20, 2015, 04:57:48 pm by Mike Sokol »
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