Shower RCD

[laurieg]

I am fitting a new electric shower and have 6mm2 twin and earth cable to fit. I have a new 30mA RCD that I want to wire in.

I am used to doing wiring but there are no wiring circuits on it. There is a black L on one of the terminals. Do I take this to be the Live terminal and the same on the output side? The RCD came with a connector block for the earth cables, which I assume I wire in seperately?

 

[andy]

I am fitting a new electric shower and have 6mm2 twin and earth cable to fit. I have a new 30mA RCD that I want to wire in.

I am used to doing wiring but there are no wiring circuits on it. There is a black L on one of the terminals. Do I take this to be the Live terminal and the same on the output side? The RCD came with a connector block for the earth cables, which I assume I wire in seperately?

1 side is for L and the other is for N. what power rating is your shower?

 

[Big_Spark]

What make is the RCD?

Ideally for a shower you should fit a DC sensing unit, these have little white cables attached to them that connects to the Earth Bar in the enclosure/DB/CU and can then monitor the actual voltage on the earth core, allowing the electronics to determine if the leakage from other sources will rise to a level that could be hazardous.

This is not required, just a suggestion.

 

[laurieg]

Thanks guys for your prompt answer. My shower rating is 10.5. Am I right in assuming that I should up the cable to 10mm2 for this power?

The RCD is a Wylex Enclosed 63A 30mA 2 pole type purchased from B & Q. It is reported as being especially for showers.

The wiring already exists from the previous installation but I felt it better to renew the cable from a junction box in the loft. (IT was rather old).

My intensions were:- junction box to RCD, RCD to switch, switch to shower. The cable to the junction box comes up from a separate CU from the main house CU with its own isolation switch.

Any good suggestions?

 

[kai]

The WYLEX RCD should be mounted next to the consumer unit - the feed cable should have its RED core wired to the Top Live Incoming Terminal, the BLACK Core wired to the other Top neutral Incoming Terminal, and the shower cable taken likewise from the Bottom Output terminals.

The Earth Cores should be connected to the Earth Terminal Block provided.

 

[Big_Spark]

Ideally there should be no junction in such a cable. You speak of a Junction Box, I hope your not referring to a round one or a unit containing 30A Connector Blocks.

10.5kW should really be on a 10mm feed, although this really depends on the run of cable, short runs will get away with 6mm, but if it is much more than about 10m from CU to shower (length of cable not direct distance) then it should be 10mm without a doubt.

The rating of the RCD is OK so long as the Overload protection in the consumer unit is matched to the load of the shower.

Remember, although an RCD of certain types may provide very basic overload protection, this is not their designed function and they should never be installed for this purpose.

Without knowing what consumer unit you have in your home I do not know if one is compatible, but I would suggest that the circuit should be protected by an RCBO instead of a MCB/RCD combination. The RCBO will give both Overload and Earth/Phase/Neutral fault protection. These can be bought in several ratings (10mA, 30mA,100mA,300mA and 500mA) they can be DC sensing, Standard, Time Delayed, DC Sensing Incorporating Time Delay and many other flavours. This scope will depend on the manufacturer of the equipment though as not all manufacturers make all possible types.

 

[laurieg]

Thanks FWL, the cable run will be about 25 feet from CU to shower so the 6mm2 should do.

You mention not using the 30A junction box. The box I have bought is a 30A terminal box. The previous installation was wire correctly from its CU and the cable is in good condition, however, the guy had wired the switch into the circuit for a bubble bath that we have got rid of.

I have removed the cable and old switches and am now left with the initial cable from the CU, (running up the inside of the wall). I was going to use the junction box to join this cable to the new run. Isn't this what they are for?

 

[Adam_151]

Kindly calculate 10500 / 230, or even 10500 / 240 , and tell me what answer you get, then tell me if you still think a 30A rated means of connection will be suitable

 

[laurieg]

Adam, apart from sarcasm being the lowest form of wit perhaps you can answer the question that I put in my last post ie. Is there any reason why I cannot, or should not, use a junction box, (at the correct rating)?

 

[plugwash]

yes you can use a junction box of appropriate rating but 30A is certainly not an appropriate rating for a shower of this size.

 

[laurieg]

Many thanks Plugwash. I stand corrected and shall hot foot it in the direction of my local B&Q. I have a 45 A switch for the circuit so why I did not get a similar junction box escapes me

 

[ban-all-sheds]

Thanks FWL, the cable run will be about 25 feet from CU to shower so the 6mm2 should do.

Never mind the length - where does the cable run? 6mm² is OK for that load when clipped direct to a surface, or buried in plaster just below the surface, but anything other than that, of if it's bunched with other cables, or runs anywhere hot (e.g. a loft space) then it won't do...

 

[laurieg]

The cable will run, clipped in a conduit, along a beam in the loft to the RCD and switch. It will then drop down into the bathroom in a conduit clipped to the wall. It will not be bundled with any other cabling.

If there is one thing my loft is not, is warm

 

[ban-all-sheds]

The cable will run, clipped in a conduit, along a beam in the loft to the RCD and switch. It will then drop down into the bathroom in a conduit clipped to the wall. It will not be bundled with any other cabling.

That's Installation Method 3, and Table 4D2A shows 6mm² as rated at 38A for that, i.e. not enough. When you go to B&Q to buy a JB, you can buy a reel of 10mm² cable instead, and replace the whole run. Which will mean you won't need a JB, which is excellent news, as AFAIK B&Q don't sell any rated at more than 30A....

If there is one thing my loft is not, is warm

Ever been up there in the afternoon of a hot day?

 

[Big_Spark]

Laurieg, unfortunately your 6mm will not do the job you want and the run will need to be upgraded to 10mm T&E.

Environmental effects always need to be accounted for, but especially on high load circuits like showers.

Incidently, you can search every B&Q in the country, you will not find a 45A rated JB in any of them. In this situation the obvious method to join the cable would be through crimps, but unless you are very familiar with crimping cables of this size, I would not advocate you do it if you did stick with the 6mm..which you most definetly should not.