Meter and test every show

Kemper Watson

Kemper Watson

Senior
Jan 11, 2011
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Atlanta, Georgia, United States
www.theplaceholders.com
I provided for a show yesterday in North Atlanta.. Stage and generator are provided by the same guy every year and I noticed he had brand new spider boxes and cabling. Just out of curiosity I metered the outlets. All was fine. Then I plugged in the polarity checker. There was a hot-neutral swap somewhere. He took apart the BRAND NEW California connectors and found not only a miswired connector but a messy job as well. He spent an hour taking apart and reconnecting his cables.. Meter and check polarity every show..
 
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Re: Meter and test every show

Kemper Watson said:
I provided for a show yesterday in North Atlanta.. Stage and generator are provided by the same guy every year and I noticed he had brand new spider boxes and cabling. Just out of curiosity I metered the outlets. All was fine. Then I plugged in the polarity checker. There was a hot-neutral swap somewhere. He took apart the BRAND NEW California connectors and found not only a miswired connector but a messy job as well. He spent an hour taking apart and reconnecting his cables.. Meter and check every show..
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We had new custom main distros, rack distros and cabling built for us. My boss went through every piece and found issues like loose neutral set screws and phase leg discontinuity (the red leg became the black leg, depending of what combination of cables, packs and drop boxes you plugged in) in about 20% of the rack packs and L21-30 cables. The vendor went of their way to make things right, though, and we're pleased with final results.

The moral of the story: test every piece of new electrical gear before putting it into service.

Another story: my boss is the FOH mixerperson for "an act popular with the scooter crowd." A few years back they played our home town festival, and were the headliners on the 4th or 5th day of the fest. He metered power and found >10v. between neutral and ground. He went to the production company (not us) and asked if there had been any problems. The PC rep said, "uh.... that's just some phase imbalance, we'll even out the loading." They did, but it made no difference. Finally my boss troubleshoots it back to the generator set, and the neutral connection is floating. In 4 days of events, either nobody from the production company or artists crews metered the power or they made a conscious decision to use a service that should have been red-tagged. The generator rental shop was called and they came out to install a bonding jumper.... that should have been in place to begin with.

The same generator shop provided power to another festival recently, and sent out a unit internally jumpered for 277/480v service. Uh... not today, fellas. They were called and they dispatched a technician lacking both knowledge and tools. Took almost 3 hours to get it put right. If you need generators in the Wichita, Kansas area do NOT rent from the company that features the brand name associated with earth moving equipment.
 
Re: Meter and test every show

Tim McCulloch said:
The moral of the story: test every piece of new electrical gear before putting it into service.
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Hell, every year we open up the AC cables and check that the connections are tight, also the distros get taken apart for the same check.

Most cables are of course completely fine. But every year we find one or two that make us say "this was a good idea", and then another that's downright frightening in how loose the wires have gotten. And if you can't check them all, at least check the ones you plug into your subs.
 
Re: Meter and test every show

Scott Helmke said:
Hell, every year we open up the AC cables and check that the connections are tight, also the distros get taken apart for the same check.

Most cables are of course completely fine. But every year we find one or two that make us say "this was a good idea", and then another that's downright frightening in how loose the wires have gotten. And if you can't check them all, at least check the ones you plug into your subs.
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I've taken to performing a "shake test" on cables before I use them. The test involves giving the connectors a good shake and listening for any rattles. Now, this only catches egregiously loose screws, but I've found a few of those over the years...
 
Re: Meter and test every show

Kemper Watson said:
I provided for a show yesterday in North Atlanta.. Stage and generator are provided by the same guy every year and I noticed he had brand new spider boxes and cabling. Just out of curiosity I metered the outlets. All was fine. Then I plugged in the polarity checker. There was a hot-neutral swap somewhere. He took apart the BRAND NEW California connectors and found not only a miswired connector but a messy job as well. He spent an hour taking apart and reconnecting his cables.. Meter and check polarity every show..
Click to expand...

Wait, how did you meter the outlets and not find a hot-neutral swap?
 
Kemper Watson said:
The meters showed the correct voltage. It was the polarity checker that showed the problem with the plugs. Unless I'm doing something wrong, that's the way I've always discovered swapped neutrals..And I"ve found a few of them.
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When you meter an outlet, do you only check between hot and neutral? You need to be metering both hot and neutral to ground as well. You would easily discover a swapped hot and neutral this way, provided you know which prong is which on an outlet.

Sent from my ADR6400L now Free
 
Re: Meter and test every show

I had some of the same issues a couple of weeks ago. Genny Co is reputable, and have been used for many years. 4 gennies on site, metered just under 8VAC N-G. Discover no bond, which I think is unusual as I was under the impression all big gennies, these were 50s, were bonded. So the guy comes back and "fixes" them. I meter again and find voltages way out, something like 180 VAC on one leg, 60 on another, and one right around 120. Investigation revealed he had tied the N & G together ON THE GROUND LUG and left the N floating on four generators. ALWAYS METER. Period.
 
Re: Meter and test every show

Jordan Ochocki said:
When you meter an outlet, do you only check between hot and neutral? You need to be metering both hot and neutral to ground as well. You would easily discover a swapped hot and neutral this way, provided you know which prong is which on an outlet.

Sent from my ADR6400L now Free
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I just read the correct way to meter an outlet. I always just metered the voltage, then threw the polarity checker after. I'll be doing it right from now on..Thanks for pointing it out
 
Matt Lillie said:
I had some of the same issues a couple of weeks ago. Genny Co is reputable, and have been used for many years. 4 gennies on site, metered just under 8VAC N-G. Discover no bond, which I think is unusual as I was under the impression all big gennies, these were 50s, were bonded. So the guy comes back and "fixes" them. I meter again and find voltages way out, something like 180 VAC on one leg, 60 on another, and one right around 120. Investigation revealed he had tied the N & G together ON THE GROUND LUG and left the N floating on four generators. ALWAYS METER. Period.
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Large generators are definitely not bonded by default, because if they are used as standby for a building the building already has neutral and ground bonded at the service.

Sent from my SCH-I545 4
 
Re: Meter and test every show

Silas Pradetto said:
Large generators are definitely not bonded by default, because if they are used as standby for a building the building already has neutral and ground bonded at the service.

Sent from my SCH-I545 4
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This provider always grounds his genny's..Always..


Edit: Which has nothing to do with the bonding post above.. Just wanted to make the statement about the provider going the extra mile to ensure the safety of his clients
 
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Re: Meter and test every show

Kemper Watson said:
This provider always grounds his genny's..Always..
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Kemper - grounding and bonding are different concepts. Grounding is sticking something in the ground. Bonding is when the neutral wire is connected to the ground wire at the point of service - either the service entrance of a building, a transformer, or a generator.

Here's Phil Graham's article on the subject:

FOH online | Generators and Portable AC Power Primer, Part 1
 
Re: Meter and test every show

Silas Pradetto said:
Large generators are definitely not bonded by default, because if they are used as standby for a building the building already has neutral and ground bonded at the service.

Sent from my SCH-I545 4
Click to expand...

Silas, I'm sure you know the below, but for the peanut gallery who have a home backup generator:

Whether or not a generator behaves as a separately derived system, and therefore the nature of the NEC bonding requirements on the genset, is ultimately a function of the nature of the transfer switch design.

A typical US home backup generator has a transfer switch that only acts on the energized legs. The collective bonding of EGC, GEC, grounding electrode, house neutral, generator egc, generator "neutral," and pole transformer center tap (i.e. incoming grounded conductor and/or neutral) is performed within the house's main service panel. Because the pole transformer center tap remains bonded, the generator in this case is not acting as a separately derived system.

Here, for the home backup case, the EGC and generator neutral are not bonded at the generator, as this would result in a current divider between the main service panel and the generator. This current divider would mean that the EGC and neutral are sharing the return current from the service panel in proportion to their respective impedances. For the backup generator case the current divider would be expected to have approximately equal currents on each of these conductors. Instead the bond between generator neutral and generator egc is performed inside the main service panel. Additionally the generator's neutral and EGC are also earthed by this panel bond connection. There is no GEC and grounding electrode at the backup generator because this generator is earthed by way of the ties to the main service panel bond point.

---

A portable generator providing power for a larger facility may be configured in the same manner as above for a home backup generator with no on-generator bonding, or it may be used with a transfer switch that causes it to act as a SDS. In the latter case the generator would then be bonded and earthed in a manner not unlike that of the main service panel.
 
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Re: Meter and test every show

I don't want to hijack the thread, but along the lines of the title of the OP, "Meter and test every show"...
Here's my story from a few weeks ago:

We show up at a commercial building set up as a senior center of sorts, but with a big hall for the concert. The building is pretty old and has several electrical closets with step-down transformers (480V to 208V), and I found a panel with some space to power up my rig. I checked the entire panel leg to leg and leg to neutral and leg to ground before I started, and the results were interesting. All hots metered to the other hots were 240V, which is very unusual on a 3-phase service, as they are normally 208V. Metering hots to neutral I got about 120, 120, and 208. If you know anything about power, you immediately know that it is a wild-leg 3-phase delta service with one transformer center-tapped to provide the neutral for two immediately adjacent hot legs. This is totally fine - not a problem as long as you only use the two 120V legs. So I proceed to tie in and everything meters great.

Next I start plugging in things and after plugging in a rack with a Furman I hear a big POP. The rack isn't on. I check the power LEDs on a few different pieces of gear and find that my subs are going crazy turning on and off. I meter again and find the voltage fluctuating wildly between about 8 and 200 volts.

The problem? Bad neutral somewhere. Not in my rig anywhere, but somewhere between the transformers and the panel I was using. The power would meter fine until I connected a load of even a 150W LED par can, when it would fall apart.

We couldn't use the power and I didn't feel like trying the other electrical closet, so we used wall power.

The only piece of gear lost was the Furman, where the MOVs failed shorted hot to ground.
 
Re: Meter and test every show

Silas Pradetto said:
I don't want to hijack the thread, but along the lines of the title of the OP, "Meter and test every show"...
Here's my story from a few weeks ago:

We show up at a commercial building set up as a senior center of sorts, but with a big hall for the concert. The building is pretty old and has several electrical closets with step-down transformers (480V to 208V), and I found a panel with some space to power up my rig. I checked the entire panel leg to leg and leg to neutral and leg to ground before I started, and the results were interesting. All hots metered to the other hots were 240V, which is very unusual on a 3-phase service, as they are normally 208V. Metering hots to neutral I got about 120, 120, and 208. If you know anything about power, you immediately know that it is a wild-leg 3-phase delta service with one transformer center-tapped to provide the neutral for two immediately adjacent hot legs. This is totally fine - not a problem as long as you only use the two 120V legs. So I proceed to tie in and everything meters great.

Next I start plugging in things and after plugging in a rack with a Furman I hear a big POP. The rack isn't on. I check the power LEDs on a few different pieces of gear and find that my subs are going crazy turning on and off. I meter again and find the voltage fluctuating wildly between about 8 and 200 volts.

The problem? Bad neutral somewhere. Not in my rig anywhere, but somewhere between the transformers and the panel I was using. The power would meter fine until I connected a load of even a 150W LED par can, when it would fall apart.

We couldn't use the power and I didn't feel like trying the other electrical closet, so we used wall power.

The only piece of gear lost was the Furman, where the MOVs failed shorted hot to ground.
Click to expand...
This is why a load test is so important and "part of this complete breakfast" of power testing.
 
Re: Meter and test every show

TJ Cornish said:
This is why a load test is so important and "part of this complete breakfast" of power testing.
Click to expand...

This is also an excellent, real world example of how you better know what the heck you are doing with power distribution. This center-tapped delta is a pretty common service, but it requires a fair amount of electrical knowledge to grok how it all functions. If the configuration is unfamiliar to you, or if it doesn't immediately spur a mental image of the wiring configuration, or if you don't immediately understand what the voltages should be (and why), then it is time to do more study of electrical distribution.
 
Re: Meter and test every show

Maybe not "by default", I can't remember the last time I had an MQ that wasn't, though. But that's why we meter every time, right? :^)

Silas Pradetto said:
Large generators are definitely not bonded by default, because if they are used as standby for a building the building already has neutral and ground bonded at the service.

Sent from my SCH-I545 4
Click to expand...
 
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