Discuss Job in a pub(shocking) in the Commercial Electrical Advice area at ElectriciansForums.net

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jackdor

Hi all, going doing a few small jobs in a pub later this week. One of which is shocking, literally. In the cellar bar they have an electric dishwasher that is on hire and has been pat tested. It is opposite a steel bottle fridge, the new landlord informs me that if you have 1 hand on either appliance and then touch the other you get a shock. both these appliances may be fed off different dis boards. the land lord has had dish washer inspected and tested by the hire company and it passed. the bottle fridge and dishwasher does not give a shock on there own. he has unplugged the dishwasher but is still using the bottle fridge. obviously there is a pd between them and some earthing issue. can you have a potential diff between the 2 earths if fed off diff dis boards or just earth fault on bottle fridge. Any ideas before i have a look. Cheers:)
 
First check the EFL of both circuits. A broken or high resistance earth could give this situation.

If both circuits are ok then I would be thinking about supplimentary bonding, but when you say two DBs, do you mean also two supplies, or 2 dbs off the same supply. If two supplies then main bonding to each other may be required.
 
First check the EFL of both circuits. A broken or high resistance earth could give this situation.

If both circuits are ok then I would be thinking about supplimentary bonding, but when you say two DBs, do you mean also two supplies, or 2 dbs off the same supply. If two supplies then main bonding to each other may be required.

Agree with Nosparks there.

Highly unlikely; but if the two DB's were fed from different sub mains then you could have different earth potentials. Not sure of the implications.
 
Apparently there are 4 large db 2 with at least 30 rcbo and mcb. The other 2 have 20 in. there are also 2 small domestic sized db. I will check earth continuity and all connection and on both dis boards. it is an old building so may have more than one supply. One of the large db supplies power for a stage(spots and sockets) but this is on the next to top floor. Thanks for your sugestions, i will let you know if it turns out to be something out of the ordinarry. cheers:D
 
You may also find the source of the p.d. may not be any of the said appliances but may be on the same circuit or board as one of them all you may be doing is creating a link to a better earth path, you can proof this by switching off the sockets but leave plugged in if the p.d. still exists its source is elsewhere but if its gone then turn each item on individually to check if it returns then you know the cause but pat test each item first yourself before you try so you know you have a good earthing to the appliances.
Also take an earth loop at each socket/spur point too to check compliance.
 
Sorted that shock job. Who ever had installed the dishwasher had made a dangerous school boy error. The washer was not on a plug but was wire into a unit containing an rcd unit. Feed in at the bottom and out let at top. All fine and well apart from they had assumed that the earth terminals at the top and bottom were connected. They were not. Resulting in the dishwasher acting like a capacitor and charging up. 4mm earth cable connecting the 2 terminals and job sorted after good testing.
cheers.:)
 

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