OT:-Earthing of fume cupboards

[John]

Hi I hope posting about a problem at work is not too off topic for this group?

We have a, built in, stainless steel, fume cupboard, in the lab. Strong salt solutions and electrical (230V) equipment (mixers, heaters, pumps etc) are used inside it.

One electrician said it should be earthed. The company that fitted it said "it is insulated so you cannot get shocks passed to earth via the casing"

So the lab manager said to me "find out which one is correct"

So HELP!!! anyone?

thanks

[Ian Stirling]

Well, if the company is wrong, somebody might get electrocuted. If the electrician is wrong, you connect a wire for no reason.

Personally, I'd earth it, if only so that I could then put an ELCB on the supply to the tools inside. I would also add an alarm to indicate that the ELCB had tripped, and a switch to defeat it (which made the alarm continuous).

This is in case it's less dangerous for faulty equipment to be operated, rather than doing the normally safe thing. If there is a door openable into the fume cabinet, I would put in series with the defeat switch two normally closed switches that open when the door does, so that faulty electrical equipment cannot be touched under power.

[raden]

In message , John writes

Have you tried asking the manufacturer?

[Badger]

Earth it and ensure the supply to the area around it as well as the fume cupboard goes through an ELCB.

Badger, lab. superintendent during the day.

[Stefek Zaba]

As a place to get a mix of somewhat informed opinions, it's OK; as a means of fulfilling your employer's Due Diligence obligations under the Electricity At Work Act and other health-n-safety legislation and established practice, it's inadequate. (Imagine the glee with which the Other Side in a tribunal/court hearing in the unwanted event of an Incident would greet "um, well, we asked about the earthing on the Net, in good ol' uk.d-i-y"...)

It's possible for one or other to be right; impulse is to guess that it needs earthing, as an Extraneous Conductive Part in IEE-Regs-speak; but the fume cupboard *might* be a "Class 2" piece of kit, wot we used to call "double insulated" in the Old Days. Even then, it's the responsibility of the designer of the entire installation to evaluate whether the design assumptions of the fume cupboard manufacturer are met in the particular installation you have - e.g. they may not have anticipated putting power sockets inside the cupboard (though it's not exactly a rarity). There are various reasonable ways to do electrical protection - one is to avoid introducing any potentials referenced to earth at all into the whole of the room/reachable area - and without knowing what your entire environment is, it's not sensible to offer specific advice. I'd try persuading your boss to shell out for a couple of hours advice from a specialist electrical contractor familiar with your industry (and whose experience is backed by professional indemnity insurance!).

HTH - Stefek

[Smudger]

I agree entirely with the above. Your employer has a duty of care to ensure that the fume cupboard is safe, and expert opinion in conjunction with a written statement from the manufacturer should be sought.

Smudger