Control Panel grounding and isolation?

busarider29 · Jan 31, 2018

Greetings from Michigan,

I am building a control panel that will be in an enclosure that will be free standing on the plant floor. I have typical 480AC 3-phase coming in to the enclosure from the overhead 480 power bus. The enclosure will be grounded via the copper ground wire off that 480 cable coming in. My question is because of that, should I, or do I need to, isolate the cabinet from the floor via rubber mats, feet, or what have you?? I'm concerned about creating a ground loop if I don't isolate the cabinet from the floor.

Thanks,
D

Plastic · Jan 31, 2018

No to rubber

busarider29 said:
Greetings from Michigan,

I am building a control panel that will be in an enclosure that will be free standing on the plant floor. I have typical 480AC 3-phase coming in to the enclosure from the overhead 480 power bus. The enclosure will be grounded via the copper ground wire off that 480 cable coming in. My question is because of that, should I, or do I need to, isolate the cabinet from the floor via rubber mats, feet, or what have you?? I'm concerned about creating a ground loop if I don't isolate the cabinet from the floor.

Thanks,
D

You are describing typical installation of industrial machinery, 480vac 3-phase 60 Hz to a machine sitting on a concrete floor in the middle of an industrial facility. The grounding conductor from the source to the panel is the single most important component of the system to protect persons and facilitate the ability for the short circuit protective device to open when there is a ground fault.

If you are concerned about ground-loops, we should review the instructions for your unique application specific controls and instrumentation devices.

Let us know what devices you ate concerned about, and forum help will follow.

Regards

kekrahulik · Feb 1, 2018

Can't say that I've ever seen a cabinet isolated from the floor. Unless you have a really unique situation / special hardware etc, I wouldn't worry about it .

busarider29 · Feb 1, 2018

Plastic said:
You are describing typical installation of industrial machinery, 480vac 3-phase 60 Hz to a machine sitting on a concrete floor in the middle of an industrial facility. The grounding conductor from the source to the panel is the single most important component of the system to protect persons and facilitate the ability for the short circuit protective device to open when there is a ground fault.

If you are concerned about ground-loops, we should review the instructions for your unique application specific controls and instrumentation devices.

Let us know what devices you ate concerned about, and forum help will follow.

Regards

I agree that this is typical installation of industrial machinery as I've done identical installations before. But considering things more for this install where I'm trying to mitigate noise issues as much as possible, I started thinking about the grounding of the equipment. To prevent ground loops, you need one and only one ground source. That ground source being the grounding conductor that comes in to the panel from the 480 VAC cable. Well, if you've got the enclosure bolted or sitting on the floor, haven't you just created a second point of grounding of the equipment, hence a ground loop?? Am I missing something here or thinking about this too much?

Cow · Feb 1, 2018

busarider29 said:
I agree that this is typical installation of industrial machinery as I've done identical installations before. But considering things more for this install where I'm trying to mitigate noise issues as much as possible, I started thinking about the grounding of the equipment. To prevent ground loops, you need one and only one ground source. That ground source being the grounding conductor that comes in to the panel from the 480 VAC cable. Well, if you've got the enclosure bolted or sitting on the floor, haven't you just created a second point of grounding of the equipment, hence a ground loop?? Am I missing something here or thinking about this too much?

You're thinking too much.

If the electrician running the circuit to your cabinet uses metal conduit with a ground wire inside, you essentially have two equipment grounding conductors right there. Not one.

If this cabinet feeds multiple pieces of metal equipment, say conveyor, or similar, with this metal equipment being attached directly to a metal building which contains an electrical service bonded to that metal building....

You see where I'm going with this? You will most likely always have multiple ground paths. This is a good thing in my opinion, it adds redundancy whether the additional ground paths are intentional or unintentional.

lfe · Feb 1, 2018

What I do:
A use a naked and isolated copper bar inside the main cabinet, to this bar arrives the grounding cable from the source supply and also connects all grounding cables from the equipment inside and outside of the cabinet, also connects the grounding cables of the cabinet enclosure with separated cable(s) for the door(s).

If the installation has secondary cabinets the system is repeated on them with a source grounding cable that comes from the main enclosure grounding bar.
... but i never isolated the enclosures itself from its support, neither the ones bolted to metallic parts.

busarider29 · Feb 1, 2018

Cow said:
You're thinking too much.

If the electrician running the circuit to your cabinet uses metal conduit with a ground wire inside, you essentially have two equipment grounding conductors right there. Not one.

If this cabinet feeds multiple pieces of metal equipment, say conveyor, or similar, with this metal equipment being attached directly to a metal building which contains an electrical service bonded to that metal building....

You see where I'm going with this? You will most likely always have multiple ground paths. This is a good thing in my opinion, it adds redundancy whether the additional ground paths are intentional or unintentional.

So the way I'm reading your answer is "yes", I'm creating a second means of grounding, which essentially creates a ground loop, but there's not much way around it.

Yes, I thought about the the equipment that will be on the floor and I agree, you've still got a means there where it will be grounded or at least contacting the floor and possibly even bolted to the floor. So in essence, having only one source of ground (literally) on the machine is going to be difficult to achieve even though in my opinion in a perfect world, that is the way it should be.

Cheers,
D

Saffa · Feb 1, 2018

If you have some sensitive electronic equipment that requires a clean Functional Earth, as opposed to a Protective Earth, then you could put in a separate instrument earth bar and run a dedicated cable directly outside to a new instrument earth.

I've never needed to do this with the stuff I work with.

dogleg43 · Feb 1, 2018

1) The cabinet needs to be solidly grounded for safety reasons.

2) A voltage rated safety mat would be used for a worker to stand on while working on something hot in the panel, along with other PPE too.

3) if an isolated ground is needed because of sensitive equipment then that is another subject.

John Morris · Feb 2, 2018

dogleg43 said:
2) A voltage rated safety mat would be used for a worker to stand on while working on something hot in the panel, along with other PPE too.

Other PPE, some companies go WAY overboard.........

for this

V0N_hydro · Feb 2, 2018

a powder coated panel bolted in to concrete or an assortment of cantruss and cable tray is a poor connection back to the 480V source neutral ground compared to a copper wire. Compare the resistance from the control panel backpan to the 480V neutral (might need really long leads for your ohmmeter) with and without the ground from the 480V supply connected (make sure there is no voltage difference first).

Control Panel grounding and isolation?

busarider29

Lifetime Supporting Member

Plastic

Member

kekrahulik

Member

busarider29

Lifetime Supporting Member

Cow

Member

lfe

Lifetime Supporting Member

busarider29

Lifetime Supporting Member

Saffa

Member

dogleg43

Member

John Morris

Lifetime Supporting Member

V0N_hydro

Member

Similar Topics