Kitchen nightmare

[nuelec]

To all you experienced fault finding electricians out there, any help appreciated on the below problem

A busy kitchen in a busy restaurant which is almost open 24/7 has a metal worktop. Kitchen staff occaisonally get minor shocks from worktop. Sockets in the vicinity are from 2 circuits. Both have been tested 1 is almost perfect. IR readings above 100 M.ohms
the other is a bit iffy (about 3.5 M.ohms from L/N to Earth.
Although low i dont deem this enough to present an immediate danger.

The shocks tend to happen whilst using portable kitchen appliances on the metal worktop. They have been tested all ok. I am guessing there is plenty of water splashing around but the staff are a bit low on detail which only adds to the problem

The worktop is not bonded but is earthed through other equipment as it is bolted to a series of other worktops & eventually to a splashback which has metal clad isolators & sockets fixed directly on it so i can only assume it is earthed through these. Hence i have 240v across worktop & live conductors of nearbye sockets.

Do I

A. remove all parrallel earth connections from the worktop. It is not an extraneaus item so is not required to be bonded
B. get to the bottom of the Low IR readings on the iffy circuit
C. Both
D. anything else?

I have been called to investigate this issue several times but never really get any headway as the kitchen is always so busy. I proposed spending a night in the restaurant without any kitchen staff in the way. But With Sunday night from midnight the only possibility for this restaurant the labour costs were too excessive for them. However very recently one member of staff recieved a serious shock which has prompted the restaurant management into action. So now i am under pressure to resolve it but it is difficult one & whatever option i choose its going to be expensive for them (Sunday night x 2 electricians) so i want to get it right

Thanks in advance for any idea's

 

[uksparks]

My 1000'th Post, here's to another 10,000 more...

Sorry, did I say that out loud!

 

[davesparks]

Right, until more information becomes available assume anyone in that kitchen is at risk of receiving a fatal electric shock.
Get them the hell out of there until the risk is removed! If the management won't do anything phone HSE.

Assuming you haven't had to involve HSE and have been allowed to investigate the fault then get yourself a wander lead and an approved voltage indicator (not a damned multimeter) and establish what voltage is present at every exposed bit of metal in the room. This may or may not help you find the fault but should assist you in avoiding receiving that fatal shock yourself!

My experience of simillar faults has almost always been traced back to a break in continuity of a cpc which has remained unnoticed until a second fault has occured (live to what was the cpc until it became disconnected)

My gut instinct is telling me that one or more of the sockets etc mounted in the metal surfaces will have no connection to the CPC of the circuit. And there is probably an appliance with a l - E fault responsible for the second fault.

Most important in all of this is to treat every exposed bit of metal in that room as live until you have proved otherwise, electricity kills.

The last one of these I had was a domestic property where the client claimed to feel a tingle when she switched the kitchen lights on. She invited me to touch the switch and see for myself, I declined. Instead a put on probe of my volt spike on a nearby socket screw and one on teh metal light switch and sure enough there was 240V between them.
Tracked it down to a metal switch in the hall where a plate screw had clipped a live, that was the second fault (her brother had fitted the metal switches recently).
Eventually found the first fault, a joint box on the lighting cct where the incoming cpc had not been connected. It was neatly pulled back where the electrician who rewired the house had stripped the T+E to connect the JB but missed the incoming one when he connected the cpc's. easy mistake to make when it was no doubt done at the end of the day in poor light and a rush to get floors back down but without any testing at the end of the job it lay there waiting for the second fault to occur some 20 years later.

 

[davesparks]

a member of staff got a belt which prompted the management into getting something done. Dont worry no one has died yet!

Now you'd better damned well make sure no-one does!

 

[nuelec]

Thanks Davesparks
Thats more what i am after, some serious suggestions to resolve a serious issue.
I did carry out a test between the worktop & other cpc's on the nearbye sockets but no voltage detected.
But what you are suggesting is that the fault could be somewhere completely different. I have been thinking that this is a possibility aswell & unlucky for me there is a lot of metal work in that kitchen to test against

 

[davesparks]

If those worktops and those cpcs are both sitting at 240V relative to earth then you won't get a voltage reading between them.

What I am saying is that there could be at least 2 faults, one a break in a cpc and 2 a live to earth short.

Oh an if I haven't mentioned it already, test every exposed bit of metal against a known good earth and make sure you do not get a shock, it's far too easy to do in a situation like this.

And it sounds like you could be in for a long night there!

 

[Engineer54]

Off the subject, on the way home I had a little job to do, fit a light in a bathroom, I mentioned it the other day but can't remover which thread, joist of it is, the old boy, his mrs died of cancer and his pull cord in the bathroom reminded him of her getting up in the night with the noise, any way, I couldn't put a switch on the outside as no rcd for new length of cable in wall.

I took his flying saucer heater thing off the ceiling tonight, replaced it with a 2D fitting and stuck a flush mounted pir next to it with the pull cord cut short near the ceiling as an over ride for the pir, looked great, bloke was well impressed, no rcd, but like for like swap execluding 6" of three core to pir.

He can now forget about his dead wife.

I take it the poor old sod doesn't have any heating in his bathroom now then??

 

[nuelec]

Davesparks
The nearbye sockets have all been tested with satisfactory Zs readings 0.3 ohms etc so i am confident that the cpc to those sockets are not sitting at 240v to earth & thus my readings between the worktop & those cps are valid i hope! unless i am missing something?

 

[jaypp]

start by turning off all circuits. check worktop. switch each breaker on one at a time (or disconnect then reconnect) till you find offending circuit. much easier to narrow it down.

EDIT; sorry, misunderstood OP. Thought worktop was 'live' -too many strongbows!

 

[davesparks]

Davesparks
The nearbye sockets have all been tested with satisfactory Zs readings 0.3 ohms etc so i am confident that the cpc to those sockets are not sitting at 240v to earth & thus my readings between the worktop & those cps are valid i hope! unless i am missing something?

I don't think you are missing anything there.
So you've established that the work tops are currently not live (I assume you tested all work tops)

Next I'd probably be looking to establish if and which of the work tops are connected to earth. Being an old fashioned type I'd be going at it with the megger for this.

I'm now expecting some of these work tops to not be connected to earth. And I'd be leaning towards a faulty appliance,

 

[davesparks]

start by turning off all circuits. check worktop. switch each breaker on one at a time (or disconnect then reconnect) till you find offending circuit. much easier to narrow it down.

need to establish what the situation is with regards which work tops are at what potential first.

 

[tazz]

Had the same in a commercial kitchen 20 years ago, turn out to be leakage from microwaves, and other appliances......we strapped 10mm earthing across every stainless steel prep table leg and back to isolator casing....cured straight away. Totally through us as all prep tables had rubber feet. Give away in the end was microwaves failed pat test (earth leakage) on prep table, but passed on wooden worktop...???

 

[uksparks]

I take it the poor old sod doesn't have any heating in his bathroom now then??

He said he didn't use it and it had been there over 25 years, he was happy with the new one as it was like a step into the future in comparison. I hate those old things, awful!

 

[Badged01]

It does seem like this forum is becoming an advice place for unqualified/very inexperienced people sometimes.

I thought that this and the DIY section was exactly for that? There is the "PUB" membership for the highly experienced and knowledgeable amongst us .......

 

[nuelec]

I have also done that & established that one section is not connected to a parallel earth. this section is next to the offending area not bolted directly to the rest of the metalwork

 

[tazz]

As I said, this baffled us, but we thought the microwaves and mixers were at fault, so we called onsite pat tester, he conducted tests and all failed, moved all equipment to wooden worktops, and all passed.....used voltsticks and neons....the tables were showing live....touch tables and no problem....use microwave, and staff complained of shocks.....bonded tables together back to isolator, and all was sorted...for your info his was Butlins in 1988, pat testing had just been introduced