# Residual Current



## robbiec202 (Aug 13, 2007)

First post

I have two portable heated food trolleys, when they are next to each other but not touching I'm getting a current reading of 118V between the two cabinets. Alternately when they are touching there is no current between them.
Thoughts please gentlemen


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## MDShunk (Jan 7, 2007)

How are you obtaining a current reading, with the units being volts?
Are the two food carts served each by seperate circuits?
Are the two food carts served each from a seperate panel?


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## JohnJ0906 (Jan 22, 2007)

These carts plug in, right? Do they have grounding plugs? 

120 volts, or something higher?


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## robbiec202 (Aug 13, 2007)

*Residual current*

Yes they plug into a 240V 16A commando plug outlet, each has it's own outlet. Using a voltmeter with a terminal on each unit reads 118V but not when measured individually.


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## JohnJ0906 (Jan 22, 2007)

Can you measure from each unit to a known ground? It sounds like one unit has a ground fault to the frame, and is not grounded. I have to admit, though, this sounds like a strange one.


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## JohnJ0906 (Jan 22, 2007)

Try testing verything you possibly can. Voltages Hot to neutral (if you have one), Hot to hot, each hot to ground, current readings on hots, neutral, and ground. Resistance from the ground pin on the plug to the frame. 

Try doing this on each unit. Write everything down.


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## MDShunk (Jan 7, 2007)

What if you put your body in the circuit... That is to say, put a finger of your left hand on one meter lead while touching one cart, and put a finger of your right hand on a meter lead while you're touching the other cart. What's your voltage reading now? If it goes to zero, you may well be measuring phantom voltage with your DMM. Some of these food carts have a pretty big element that snakes all through the cart. It could induce phantom voltage on the frame in a fantastic way, I suppose.


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## robbiec202 (Aug 13, 2007)

Absolutely, thats exactly what it seems to be if you touch them together and read the voltage it disappears until you let go. Had a chap say's he got a belt off it but it could have been static but I had to check before I could allow them to re-use the units. I have bonded them together until I can find the reason for this. But your explanation is a sure possibillity as each unit is individually earthed.
Thanks

Regards

Robbiec202

*"You can lead a horse to water but a pencil must be led":whistling2: *


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## frank (Feb 6, 2007)

Robbie

You may have an induced voltage from one of the heater trays' (Inductance) No current circulating. You would not get this effect though if the trays were earthed. My first worry is as mentioned above that you have an earth fault to chassis that is of high value impedance and therefore insufficient fault current is present to activate a circuit breaker/fuse. Bonding one to the other neutralises the residual or inductive component via a GOOD earth path present in one or other of the trays.
In any event. You should not use them until you have solved the problem. Bonding them together is not a cure. 

I suspect that if you use a voltmeter between the frame of one tray and connect the other lead to the Commando Earth ( check that this is a good earth) you will identify the faulty tray.

Frank


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## robbiec202 (Aug 13, 2007)

*Frank*

Thanks for this, I have now taken them out of service until a thorough check can be done. Will let you know when I find the fault.

*"You can lead a horse to water but a pencil must be led":whistling2: *


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