Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Peter Kowalczyk]

Hey Team,

I did an event a while back on Generator Power.  The wedding coordinator rented a trailer generator (way overkill for our needs actually), which was dropped off with no instruction or 'configuration'

I routed their 50A cable to my distro, got it running, measured no output, RTFM to find the switch setting that needed to be changed, and finally measured correct voltage at my end. 

In the process, I noticed that the generator was not actually 'Earthed' - as in, connected to a metal rod pounded into the ground.  I was under the impression that providing a current path into the actual ground via a metal earth rod was standard operating procedure.   

I alerted the coordinator to what I saw as a safety concern, who called the rental provider, who said something to the effect of 'We never do that, it's fine.'  RTFM again an notice a line that says that an earth rod is required if the generator is to power a permanent structure... but nothing about portable use.

Was I wrong to raise a concern?  Under what circumstances would you consider this earth rod a hard requirement, vs. no big deal?

Thanks.  (flame suit on ....  or maybe in this case, I'll climb in my faraday cage to await your responses...)

[Brian Jojade]

'We never do that, it's fine.'

That's on the same line as those that lop off ground pins.  Nobody has died... YET.

[Steve-White]

'We never do that, it's fine."

That's on the same line as those that lop off ground pins.  Nobody has died... YET.

When somebody gets lit up real nice and their insurance underwriter refuses to pay due to negligence, they'll reconsider that stance - even before the lawyers, expert testimony and judgement concludes.

[Tim McCulloch]

Hey Team,

I did an event a while back on Generator Power.  The wedding coordinator rented a trailer generator (way overkill for our needs actually), which was dropped off with no instruction or 'configuration'

I routed their 50A cable to my distro, got it running, measured no output, RTFM to find the switch setting that needed to be changed, and finally measured correct voltage at my end. 

In the process, I noticed that the generator was not actually 'Earthed' - as in, connected to a metal rod pounded into the ground.  I was under the impression that providing a current path into the actual ground via a metal earth rod was standard operating procedure.   

I alerted the coordinator to what I saw as a safety concern, who called the rental provider, who said something to the effect of 'We never do that, it's fine.'  RTFM again an notice a line that says that an earth rod is required if the generator is to power a permanent structure... but nothing about portable use.

Was I wrong to raise a concern?  Under what circumstances would you consider this earth rod a hard requirement, vs. no big deal?

Thanks.  (flame suit on ....  or maybe in this case, I'll climb in my faraday cage to await your responses...)

"We never do that..." means "the ground rods never come back, the grounding wire never comes back." 

Mostly they don't do it because clients take care of earthing as part of a larger electrical site design, or they ignore it, or they use the provided multipole outlets on the generator to power "plug and cord" tools/appliances/stuff (permitted use without an earth ground).  In that regard, some may consider a construction 'spider box' with individually protected GFCI outlets 'for use by personnel', as such a plug and cord load although I don't think the rest of code considers it that way.

Potentially relevant Code citations: all of article 445; 250.34, 250.35, 250.112 from the index to the 2017 NFPA 70a.

[Mac Kerr]

In the process, I noticed that the generator was not actually 'Earthed' - as in, connected to a metal rod pounded into the ground.  I was under the impression that providing a current path into the actual ground via a metal earth rod was standard operating procedure.   

I alerted the coordinator to what I saw as a safety concern, who called the rental provider, who said something to the effect of 'We never do that, it's fine.'  RTFM again an notice a line that says that an earth rod is required if the generator is to power a permanent structure... but nothing about portable use.

Was I wrong to raise a concern?  Under what circumstances would you consider this earth rod a hard requirement, vs. no big deal?

Thanks.  (flame suit on ....  or maybe in this case, I'll climb in my faraday cage to await your responses...)

That ground rod will give you good protection against lightning. If you have a metal stage, it should also have a ground rod. Neither will offer much protection from an electrical fault, that's the job of the ground connection in the distro. You can't sink an appreciable amount of electricity into dirt. It works with lightning because it allows the huge electrical charge in the cloud to short to the corresponding opposite charge that accumulates on that dirt in response to the charge on the cloud.

Mac

[John Roberts {JR}]

When in doubt I advocate for using GFCI protected power drops to help keep the meat puppets breathing.

JR

[Stephen Swaffer]

That ground rod will give you good protection against lightning. If you have a metal stage, it should also have a ground rod. Neither will offer much protection from an electrical fault, that's the job of the ground connection in the distro. You can't sink an appreciable amount of electricity into dirt. It works with lightning because it allows the huge electrical charge in the cloud to short to the corresponding opposite charge that accumulates on that dirt in response to the charge on the cloud.

Mac

Mostly true-but that depends a lot on the moisture content of the earth.  I once managed to create a fault from a POCO transformer that caused sparks between a ground rod and a ground wire a helper was in the process of connecting connecting.  Most code requirements are driven by statistics-no one wants to be the statistic that causes another code rule!

[Frank Koenig]

Mostly true-but that depends a lot on the moisture content of the earth.  I once managed to create a fault from a POCO transformer that caused sparks between a ground rod and a ground wire a helper was in the process of connecting connecting.  Most code requirements are driven by statistics-no one wants to be the statistic that causes another code rule!

When I was growing up, whenever the furnace blower kicked on the lights would dim a little. One day I observed that the lights got brighter when the furnace came on. This slowly got worse over the course of weeks. It turned out that the neutral conductor in the service drop from the pole to the house had broken and all that was keeping the house from totally unbalancing was the ground conduction between the POCO ground rod at the distribution transformer pole and the water-pipe ground at the house service entrance. It was winter in a valley bottom (San Francisco Bay) with a shallow water table and the galvanized steel service pipe most likely ran not too far from the pole but still... I doubt the outcome would have been as good up on a fan in the Mojave Desert.

--Frank

[ProSoundWeb Community]