current on ground

[mnbiker]

Just finished a install on a new oven here at work. 192 kw at 480 volt. I took some current reading at first start up. all phase conductors were at specs. I noticed the grounding conductor had about 2.5 amps on it. I check other grounding wire in control cabinet, the grounding wires going to the wattlow controls each had between .2 and .4 amps each, which adds up to 2.5 I have on the main grounding wire going back to switch gear.

is this consider objectionable or acceptable.

thanks

 

[growler]

I think I would call the company that built the oven and see what they think. They may need to send a service tech to check internal wiring. Get the name of whoever you talk to and make sure there is a record of the report.

I don't see this as the electrican's problem other than to report your findings.

 

[mnbiker]

the oven Tech was on site and I sent email to the oven company to see what they had to say.

 

[mnbiker]

here is the response I received from their electrical engineer; being the plant electrician I am not happy with it.


Please see the following response from our electrical engineer. While Scott ( Service Technician) was onsite, he could find nothing wrong on the oven equipment.

It is a hard to answer what is acceptable, typically less than 1A or maybe less pending on the grounding system and whether or not you have unbalanced load current and possibly plant power.

It could possibly be objectionable current. You shouldn’t have current flowing on grounding conductor. You may have some leakage from devices but it will be very minimal in milli Amps. I don’t know how every machine in there plant is grounded and how the bonding paths are. They may get nuisance tripping on ground fault protection devices in the panel.

Is there a floating ground? (Scott) could not find any How are they measuring current? (Scott) Using an Amp Clamp on ground wire.

Please let us know if you have any additional questions or concerns. Thank you.


any thoughts would be appreciated.

 

[growler]

here is the response I received from their electrical engineer; being the plant electrician I am not happy with it.


It could possibly be objectionable current. You shouldn’t have current flowing on grounding conductor. You may have some leakage from devices but it will be very minimal in milli Amps. I don’t know how every machine in there plant is grounded and how the bonding paths .

Is there a floating ground? (Scott) could not find any How are they measuring current? (Scott) Using an Amp Clamp on ground wire.

Thank you for sharing the responce of the manufacturer. I always find their comments interesting if not overly helpfull.

He may have a point about the amp clamp since we don't know how accurate that is. I don't see why the service tech didn't use his own equipment since he was on site.

I think that I would take the ground loose from the oven and measure voltage from the frame to ground and see what that is. I would use my meter (in line ) to measure current flow from frame to ground.

I guess you could use your amp clamp to check the grounds on other machines just to see if you get a reading that high.

 

[mnbiker]

I think that I would take the ground loose from the oven and measure voltage from the frame to ground and see what that is. I would use my meter (in line ) to measure current flow from frame to ground. [/FONT]

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I will check to see if the they will let me check that, but it will take some work as the feed is in a 3 inch conduit back to the switch gear. I am assuming that there is about the same amount current flowing on the conduit as the equipment grounding conductor.

I had the tech verify with his amp clamp the same reading I had with mine.

 

[growler]

I check other grounding wire in control cabinet, the grounding wires going to the wattlow controls each had between .2 and .4 amps each, which adds up to 2.5 I have on the main grounding wire going back to switch gear.

is this consider objectionable or acceptable.

thanks

I will check to see if the they will let me check that, but it will take some work as the feed is in a 3 inch conduit back to the switch gear. I am assuming that there is about the same amount current flowing on the conduit as the equipment grounding conductor.

I had the tech verify with his amp clamp the same reading I had with mine.

Sorry I didn't even think about the conduit.

Maybe you could check the ground to one of the controllers (.4 amp) because that does seem high, Even their engineer seems to think that it should be milli amps.


At least you can print out a copy of their responce to show you informed the manufacturer of a possible problem and you did get a reply.