Grounding Electrode Conductors

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Grouch

Grouch

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New York, NY
Hi All,
I'm working on a project at a hospital where they want to bring in this huge cancer fighting machine. The power feed to the machine will be a 90 amp, 480 volt, 3 phase feeder, with several other 120 volt, 20 amp circuits feeding lights / receptacles / miscellaneous equipment.

The vendor of the machine tells me that I had to make sure the electrical service to the building was not grounded to the cold water pipe... a GEC connection to the cold water pipe would introduce electrolysis, thereby affecting the machine. I verified with the building engineer that the building is in fact connected to the cold water pipe, building steel, and a ground rod... so there are 3 grounding electrodes. According to the vendor, this is still a problem, since the cold water pipe is one of the grounding electrodes.

Question: am I allowed to cut the connection to the cold water pipe, thereby eliminating the problem??? I would assume yes, since the service is grounded to 2 other grounding electrodes... building steel and the ground rod, so there is redundancy. Would the code allow this? I would actually be scared to show something like this on a set of drawings. if cutting the connection to the cold water pipe is not allowed, what other solution is there?

Thanks!
 
Based on 250.50 I would say no you can't cut the water bond.

Wondering if setting a seperate transformer for this piece of equipment say an isolating transformer (I think that's what they are called) would help you comply with the requirements. Although not quite sure how electrolysis enters into the equation. Maybe someone can explain that?
 
cmreschke said:
Based on 250.50 I would say no you can't cut the water bond.

Wondering if setting a seperate transformer for this piece of equipment say an isolating transformer (I think that's what they are called) would help you comply with the requirements. Although not quite sure how electrolysis enters into the equation. Maybe someone can explain that?
Click to expand...

yes, that's another question i also had! How does electrolysis come in and what does it affect actually!?
 
Electrolysis happens when the metal of the pipe is in contact with the minerals, etc. in the earth surrounding the building.
It can cause currents to flow and an offset in the voltage of the pipe compared to the natural earth voltage.
One possibility would be to insert a dielectric coupling in the main water feed to the building, making it no longer a grounding electrode, but rather just another large bunch of metal that needs to be bonded to the grounding electrode.

Are they also asking you to provide a separate earth electrode for the equipment, or an isolated ground back to the main bonding jumper location?
The former is problem-causing superstition that violates the NEC, the latter is of dubious value but would at least do no harm.

P.S.: If they are worried that their machine produces excessive current, perhaps even DC, in the EGC connection that can cause corrosion of the water pipe, rather than the electrolysis interfering with the machine, that would at least make sense. But it would also mean that the machine is violating the NEC and could cause a GF detector or RCD to trip.
 
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I wold tell the vendor that the GES is installed according to the NEC and any problems with the water pipe connection are his. Even if you remove the GEC from the water pipe could you really isolate the entire water system from a connection to the other electrodes?
 
iwire said:
Electrolysis is not an issue with AC power as far as I know
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I think the vendor has it backwards. They are worried that their machine will cause electrolysis in the water pipe. They should ground the machine with an isolated ground, this is not a questionable practice like the previous poster mentioned. It's questionable on today's computers, not equipment like this because it protects the rest of the building from this stray DC voltage that is known to exist on the ground. (electrolysis is performed with DC current into water)

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It has been my experience with a few medical equipment manufacturers that they have no clue and this outfit sounds like a perfect example of one of them.

Roger
 
Sounds like the machine needs better design to isolate itself from causing problems.

If you run an EGC to it, it ultimately will be bonded at some point to water piping, building steel, other metal components. Even if you sever intentional grounding electrode conductors and bonding jumpers, there often is other natural paths between a lot of those components.
 
How could electrolysis in the ground connection be a problem unless the equipment is intentionally pushing current onto the EGC, which it shouldn't do, right?
 
ggunn said:
How could electrolysis in the ground connection be a problem unless the equipment is intentionally pushing current onto the EGC, which it shouldn't do, right?
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Right but the problem with the manufacturers engineers is that they don't understand building wiring systems. For years I fought with a certain manufacturer that always wanted a 1/0 neutral pulled and left in a gutter not connected to anything, finally we had a project that was going to require demoing walls for a feeder that was going to be in the neighborhood of 200' and they wanted (5) 1/0 conductors (yeah, they want the EGC the same size as the circuit conductors) however, if this 1/0 feeder could be changed to #1 conductors an existing conduit could be used. The building design engineer, owner, and myself set up a meeting to have one of their engineers onsite to which we got a salesman and the installer. After arguing about the 1/0 conductors being extreme overkill for a 60 amp peek surge (the machine ran at about 15 amps in most procedures) they agreed to let the owner have a smaller feeder, the #1s. When they finally connected the feeder to their equipment they left the neutral in the gutter with the end taped, the owner wanted to know what they intended to do with it since it almost caused a major construction project, they told the owner that their engineers said it worked as a shield and had to be there.
:jawdrop:

I don't know if it held true but the owner said they would never purchase another machine from this manufacturer again.

Roger
 
310 BLAZE IT said:
hey should ground the machine with an isolated ground, this is not a questionable practice like the previous poster mentioned. It's questionable on today's computers, not equipment like this because it protects the rest of the building from this stray DC voltage that is known to exist on the ground. (electrolysis is performed with DC
Click to expand...

Can you explain what you mean? If you are suggesting a ground independent of the grounding electrode system, you do know that would violate the NEC?


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roger said:
I don't know if it held true but the owner said they would never purchase another machine from this manufacturer again.
Click to expand...

I have run into a lot of OEM people that think bonding the neutral to ground in multiple locations, isolated grounds (whatever they mean by that), or adding ground rods will solve all kinds of problems. I try not to get real excited about it anymore.
 
petersonra said:
I have run into a lot of OEM people that think bonding the neutral to ground in multiple locations, isolated grounds (whatever they mean by that), or adding ground rods will solve all kinds of problems. I try not to get real excited about it anymore.
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They have seen those type of things solve (in reality mask) a problem in the past, therefore it is now the way to do it in their eyes.
 
Thanks everyone for your responses... Sorry for coming back late, was at a meeting all day. In the meantime, I did call back the manufacturer to confirm if the cold water pipe connection affected the machine or vice versa just to make sure.... He said again that it's the machine that gets affected. When I asked for an explanation unfortunately, he wasn't sure how, it's just what he's told by his engineers.

golddigger asked if the vendor asked for a separate earth electrode to the machine... The answer is no. All they say is we can't be connected to the cold water pipe.

so say I use an isolation transformer with an isolated ground going to the machine. Would this alleviate the problem? (If there is one). But I would still have to ground the secondary of the transformer to building steel... Wouldn't building steel be bonded to the cold water pipe anyway, in which case I'm back to square one?
 
Grouch1980 said:
so say I use an isolation transformer with an isolated ground going to the machine. Would this alleviate the problem? (If there is one). But I would still have to ground the secondary of the transformer to building steel... Wouldn't building steel be bonded to the cold water pipe anyway, in which case I'm back to square one?
Click to expand...

Yup.
 
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