Supplementary bonding to bathroom heater

[drood]

I am installing a convection heater into a bathroom in zone 3. There is no obvious way to connect the earth wire, so could i secure it with a self-tapping screw into an unobtrusive part of the casing and take it back to the earth terminal in the FCU?

Many thanks in advance.

 

[ban-all-sheds]

1) If it has no earth connection then either it doesn't need one, or it is a nasty dangerous item that should not be used.

a)On the assumption that it's a reputable make, and carries stickers indicating that it meets BS/EN standards, or is CE marked or has BEAB approval etc, see if it has the symbol for a double-insulated appliance (a square within a square), or see what the instructions say about earthing. If it is double insulated, it does not need an earth, and attaching one might make it less safe.

b)If you bought it cheap in the market, or it was left to you by your dear old gran, or you found it in a skip, and it has no comforting safety labels, don't use it.

2)Taking a connection back to the CU as you describe would not be supplementary bonding, it would be earthing. Supplementary bonding would be connecting the earth conductor of the appliance to the bonding in your bathroom, not the CU earth.

 

[drood]

Thanks for your input - Ban all sheds.

I guess I should have been clearer in my question though. The heater is a new Dimplex. I understand that the IEE Wiring Regs (16th Ed) state that all exposed metalwork in all bathroom zones must be bonded to the supplementary earthing system regardless of the class of the item installed. The heater is indeed double insulated but the casing should still be bonded to the supplementary bonding within the bathroom.

The regs also indicate that it is sufficient to bond the casing to the earth terminal in the FCU (Fused connection unit) supplying the unit, not the CU (Consumer Unit) - I think you misread my original post - to reduce unsightly cables running to the next item in line.

My setup is as follows: switched fused connection unit (SFCU) on spur outside bathroom, from adjoining bedroom socket. Connection from there to flex outlet plate alongside heater inside bathroom. I was proposing to connect the supplementary bonding to the casing of the heater and run the cable to the SFCU outside the bathroom.

Is this acceptable?

Thanks again.

 

[ban-all-sheds]

This debate rages on.

The regs require the bonding of extraneous-conductive-parts, not "all exposed metalwork".

The definition of an "extraneous-conductive-part" is

A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.

so I would maintain that the casing of your double-insulated Dimplex radiator is no more an e-c-p than is a metal door handle, or toothbrush holder or towel ring, or shelf bracket, or CH radiator fed by plastic pipes, etc etc etc.

So it should not be connected to the supplementary bonding. In fact, doing so would in effect be earthing a Class II appliance, which you should not do.

However, you should connect the incoming earth in the FCU to the rest of the bonding, in case anybody ever introduces a Class I appliance in place of the Class II. And apologies for the CU/FCU mixup - doh!

 

[securespark]

This from NIC pubn "snags and solutions in earthing & bonding"

Most often, rads metal window frames ducts etc, will not be extraneous conductive parts, as defined in 7671, and where this is the case, will not require main or supp bonding.

Is the item conductive?

Is the item liable to introduce a potential?

Is the item part of the elec. inst.?


On different topics, the book says:

Supp. bonding to a metal kitchen sink is NOT required. This will upset Jim terribly!

It is NOT required to run a conductor back to the main earth terminal to link supp bonding in bathroom to main bonding.

There is an exception: if the metal water service pipe enters in the bathroom and protection against indirect contact is via EEBAD, the pipe must be connected to the main bonding as per 413-02-02. Further, in this location, it would also require supp bonding.

 

[ban-all-sheds]

That's not an exception - you still aren't running the supplementary bonding back to the MET, it's the main bonding.

 

[securespark]

I suppose not, but if you are connecting a main bond and supp bond to same pipe, there is a more direct path.

Some more from the book:

(they are talking about an electric towel rail here, but I suppose the same applies to other Class 1 appliances)

It is not usually necessary to provide additional supp bond - the cpc in the cord often meets the requirements of regs. But, supp bond may be needed between the earth term in the conn unit and other ecp's in the bathroom if req'd by reg 601-04-01.

However, as the appliance queried in this post is double insulated, no bonding of the casing is necessary.

As Ban says, in certain situations earthing double insulated equipment can make for an unsafe installation, rather than a safer one.

 

[drood]

Thanks to both of you - very interesting and helpful.