Electrical Engineering - Power generator and mains grounding?

Author

Power generator and mains grounding?

John E.

2006-08-18, 5:25 pm

At an outdoor event consisting large tents (plywood floors, metal tubular
frame, poly tenting), air-conditioning, lighting and public address system is
powered by a trailer-mounted 3-phase (208 v) generator. The generator rental
place drove a ground rod and connected its ground connector there.

Event organizers ran audio & video system of the generator. TV cables, and
telecom cables were run from a business building and used with the audio &
video system. (All except air-conditioning are single-phase 120v.)

Ground loop issues became apparent with difference between the 2 grounds (the
utility and the generator). Switched audio & video power to the utility power
to help solve the issue.

But now the issue of grounding comes up as we add wiring and switch boxes for
the lighting (powered by the generator) that will be near the audio & video
control station (powered by the utility via the building).

To be safe, should these 2 grounds be tied together? Where?

If this turns out to be beyond our abilities to solve we will call in a
electrician, but if it is as simple as tying the grounds together there isn't
a need, is there.

All constructive suggestions are appreciated.

Thanks much,
--
John English

gfretwell@aol.com

2006-08-18, 5:25 pm

On Fri, 18 Aug 2006 14:39:48 -0400, John E. <incognito@yahoo.com>
wrote:

>At an outdoor event consisting large tents (plywood floors, metal tubular
>frame, poly tenting), air-conditioning, lighting and public address system is
>powered by a trailer-mounted 3-phase (208 v) generator. The generator rental
>place drove a ground rod and connected its ground connector there.
>
>Event organizers ran audio & video system of the generator. TV cables, and
>telecom cables were run from a business building and used with the audio &
>video system. (All except air-conditioning are single-phase 120v.)
>
>Ground loop issues became apparent with difference between the 2 grounds (the
>utility and the generator). Switched audio & video power to the utility power
>to help solve the issue.
>
>But now the issue of grounding comes up as we add wiring and switch boxes for
>the lighting (powered by the generator) that will be near the audio & video
>control station (powered by the utility via the building).
>
>To be safe, should these 2 grounds be tied together? Where?
>
>If this turns out to be beyond our abilities to solve we will call in a
>electrician, but if it is as simple as tying the grounds together there isn't
>a need, is there.
>
>All constructive suggestions are appreciated.
>
>Thanks much,

The short answer is you should tie all grounding electrodes on a
property together with 6ga copper conductors. We don't have enough
information yet to answer how you are grounding the neutral but if
everythig is tied together you will be using the main bonding jumper
in the service disconnect and that is sufficient. You only want one
place where the white and trhe ground get connected but you can have
the ground electrrode system itself connected as many places as you
like.
Pick a single source and a single ground connection for all of your
audio equipment to minimize the hum problems. You still may end up
with isolation transformers on the audio side connections.

Dale Farmer

2006-08-19, 3:25 am

John E. wrote:
> At an outdoor event consisting large tents (plywood floors, metal tubular
> frame, poly tenting), air-conditioning, lighting and public address system is
> powered by a trailer-mounted 3-phase (208 v) generator. The generator rental
> place drove a ground rod and connected its ground connector there.
>
> Event organizers ran audio & video system of the generator. TV cables, and
> telecom cables were run from a business building and used with the audio &
> video system. (All except air-conditioning are single-phase 120v.)
>
> Ground loop issues became apparent with difference between the 2 grounds (the
> utility and the generator). Switched audio & video power to the utility power
> to help solve the issue.
>
> But now the issue of grounding comes up as we add wiring and switch boxes for
> the lighting (powered by the generator) that will be near the audio & video
> control station (powered by the utility via the building).
>
> To be safe, should these 2 grounds be tied together? Where?
>
> If this turns out to be beyond our abilities to solve we will call in a
> electrician, but if it is as simple as tying the grounds together there isn't
> a need, is there.
>
> All constructive suggestions are appreciated.
>
> Thanks much,
I do this stuff all the time. There are a couple of solutions you
work on, depending on the money/time/personalities involved.
First option: Go with 100% generator power or 100% shore power for
everything. Second option: ( which is what you already did) Put all
the audio and video stuff on one and only one source of power. Third
option, have the audio and video folks put isolation transformers on all
their signal lines that connect from the generator power system to the
utility power system. Fourth option: Run a heavy gauge conductor from
the ground stake at the generator and connect it to the utility power
ground, making it all one ground system.
You need to work with your local electrical inspector, as what you
want to do has some non-obvious hazards, and they are not normal
electrical practice. You don't mention where you are located, as the
rules vary from country to country. If you are in the US, I'll come out
for a suitable day rate and expenses to consult on the issues. *grins*

--Dale

tim gorman

2006-08-19, 9:25 am

gfretwell@aol.com wrote:

>
>
> On Fri, 18 Aug 2006 14:39:48 -0400, John E. <incognito@yahoo.com>
> wrote:
>
>
> The short answer is you should tie all grounding electrodes on a
> property together with 6ga copper conductors. We don't have enough
> information yet to answer how you are grounding the neutral but if
> everythig is tied together you will be using the main bonding jumper
> in the service disconnect and that is sufficient. You only want one
> place where the white and trhe ground get connected but you can have
> the ground electrrode system itself connected as many places as you
> like.
> Pick a single source and a single ground connection for all of your
> audio equipment to minimize the hum problems. You still may end up
> with isolation transformers on the audio side connections.

If the generator ground and the building ground are of different enough
potential to cause you voltage problems in the ground loops then just
running 6ga conductors between them may not fix your problem either. It
would depend upon how long of a run you would have to make to attach the
two grounds together. You might just be better off running a 6ga conductor
to the building ground and using that as your grounding point for
everything.

tim

DaveC

2006-08-20, 9:25 am

OP, here.

Since the 2 supplies are in all other respects separate, shouldn't the
neutral be tied to the ground for each supply even though the grounds are (or
will soon be) common?

Another question: Where should the grounds be connected? The generator is
about 75 yards from the building (permanent structure) with the tents between
the two. Simplest is to run a conductor from the generator's ground conductor
where it reaches the tent (at the load), to the service entrance of the
building.

Also, should the generator's ground -- connected to the ground rod at the
generator -- be disconnected in lieu of the ground rod at the utility service
entrance? Or is it "the more, the merrier" when it comes to ground rods? (The
tent skeleton has its own ground rod, too, BTW, not connected to any
electrical ground.)

In Maryland, USA, near Bethesda.

Thanks much,
--
John English

John E.

2006-08-20, 9:25 am

Thus spake DaveC:

> Also, should the generator's ground -- connected to the ground rod at the
> generator -- be disconnected in lieu of the ground rod at the utility service

> entrance?

To clarify: Should the generator's ground... be disconnected *from the ground
rod at the generator*...?

--
John English

sQuick

2006-08-20, 8:25 pm

"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C10B81B4001201C9F02845B0@news.readfreenews.net...
> At an outdoor event consisting large tents (plywood floors, metal tubular
> frame, poly tenting), air-conditioning, lighting and public address system
> is
> powered by a trailer-mounted 3-phase (208 v) generator. The generator
> rental
> place drove a ground rod and connected its ground connector there.
>
> Event organizers ran audio & video system of the generator. TV cables, and
> telecom cables were run from a business building and used with the audio &
> video system. (All except air-conditioning are single-phase 120v.)
>
> Ground loop issues became apparent with difference between the 2 grounds
> (the
> utility and the generator). Switched audio & video power to the utility
> power
> to help solve the issue.
>
> But now the issue of grounding comes up as we add wiring and switch boxes
> for
> the lighting (powered by the generator) that will be near the audio &
> video
> control station (powered by the utility via the building).
>
> To be safe, should these 2 grounds be tied together? Where?
>
> If this turns out to be beyond our abilities to solve we will call in a
> electrician, but if it is as simple as tying the grounds together there
> isn't
> a need, is there.
>
> All constructive suggestions are appreciated.
>
> Thanks much,
> --
> John English

Just to point out, If this was a UK installation, the power
supply company would have some major issues with the
grounds/earths & neutrals being tied together.

sQuick..

Spokesman

2006-08-20, 8:25 pm

"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C10B81B4001201C9F02845B0@news.readfreenews.net...
> At an outdoor event consisting large tents (plywood floors, metal tubular
> frame, poly tenting), air-conditioning, lighting and public address system
is
> powered by a trailer-mounted 3-phase (208 v) generator. The generator
rental
> place drove a ground rod and connected its ground connector there.
>
> Event organizers ran audio & video system of the generator. TV cables, and
> telecom cables were run from a business building and used with the audio &
> video system. (All except air-conditioning are single-phase 120v.)
>
> Ground loop issues became apparent with difference between the 2 grounds
(the
> utility and the generator). Switched audio & video power to the utility
power
> to help solve the issue.
>
> But now the issue of grounding comes up as we add wiring and switch boxes
for
> the lighting (powered by the generator) that will be near the audio &
video
> control station (powered by the utility via the building).
>
> To be safe, should these 2 grounds be tied together? Where?
>
> If this turns out to be beyond our abilities to solve we will call in a
> electrician, but if it is as simple as tying the grounds together there
isn't
> a need, is there.

For an event of this magnitude and in the interests of public safety
you should have an electrician doing the work for you or at least
supervising and planning the work you are doing.

>
> All constructive suggestions are appreciated.
>
> Thanks much,
> --
> John English
>

Homer J Simpson

2006-08-20, 8:25 pm

"DaveC" <me@privacy.net> wrote in message
news:0001HW.C10DC63A0001591CF02845B0@news.readfreenews.net...

> Also, should the generator's ground -- connected to the ground rod at the
> generator -- be disconnected in lieu of the ground rod at the utility
> service
> entrance? Or is it "the more, the merrier" when it comes to ground rods?
> (The
> tent skeleton has its own ground rod, too, BTW, not connected to any
> electrical ground.)

Don't even think of doing this without a skilled and experienced
electrician. Don't be surprised if he contacts the utility for further
assistance.

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