The OSG seems vague about whether to to install a shower in a bathroom on the rcd side of a split board. The shower would be in zone 1 but i cant seem to find clarification of the connection to a consumer unit and are there variations for supply system TT TNs TNCS .any help much appreciated .
I think it has become the norm' to have such equipment installed to a safe supply, so an RCD fits the bill most effectively.
On 20 May 2004 17:29:16 GMT, in uk.d-i-y snipped-for-privacy@aol.com (Wheelbarrowbob) strung together this:
There's a thread on this started the other day. A shower doesn't neccesarily need RCD protection, but it has become common practice to fit one. I haven't fitted a shower without one.
It all comes down to maxium disconnection times. (0.2s IIRC). The disconnection time is function of
1) The supply impedance (whose macximum valve will vary between different type of installation). 2) The size and lengh of the supply and CP conductors in the shower supply cable 3) The type of fuse/MCB used to protec tthe circuit.It is possible to design regular shower circuits without using an RCD but it required less thought and a little more work and money to install an RCD or RCBO unit.
Hence the norm is to use an RCD or use the RCD side of the 'panel'.
The reason i posted the origional question was because a builder mate of mine has been working on 3 barn conversions and the devolper did his own electrical installation and wants it certified., asking questions 2 things strike me as peculiar, the supply to one buildings consumer unit has been run in SWA 30 metres from the meter, and a 8.5 KW shower kept tripping the rcd so he phoned triton and they told him to swap the supply to the non rcd side of the board and its protected by a 32A trip.Need i say any more !
I hope the installation was megged and tested properly. There's no reason for a shower to blow an RCD, although it may do so temporarily if it has been stored for some time, as heating elements sometimes need to be turned on for 20 minutes to expel moisture so that they become sufficiently electrically insulating. If this is the case, then after a few showers, you may find that it is happy back on the RCD side with no trips.
Christian.
Vague? The OSG is actually very clear about what should be c "30mA RCDs installed to provide protection to socket-outlets likely to feed portable equipment outdoors should protect only those sockets, see Fig 3b."
Fig. 3b shows an example of a split-load CU with five circuits on the non-RCD side and only two circuits on the RCD side. Footnotes label the non-RCD circuits as "lights, cooker, water heating, smoke alarms," and the RCD circuits as "circuits to portable equipment outdoors and socket-outlets that may reasonably supply equipment outdoors."
You can't get much clearer than that :-)
The only reason to RCD-protect an electric shower would be where the earth fault loop impedance is too high to achieve the required disconnection time, which is 5 seconds [1]. Obviously this will always apply in TT installations, but with TN earthing, reliance on an RCD should be avoided by design - protection by means of the overcurrent device is more reliable.
Table 7.1 in the OSG is your friend; it gives the maximum circuit lengths which are OK, without recourse to an RCD, for various types and ratings of MCB or fuse. For example:
------------------------------------------ Max. cct. length for earthing type
------------------------------------------ Device Rating TN-S TN-C-S
------ ------ ---- ------ Type B MCB 40A 51m 53m
Cartridge fuse 45A 10m 49m Rewireable fuse 45A 49m 49m Type B MCB 45A 35m 49m
------------------------------------------
The importance of ensuring that the correct main and supplementary earth bonding is in place when installing an electric shower cannot be stressed too highly. It is on that that your life depends in the event of an earth fault. Correct bonding is both cheaper and more reliable than an RCD.
[1] The former long-standing requirement for 0.4s disconnection for fixed equipment in bathrooms was removed in the 2000 amendment to BS 7671:1992 (the amendment that introduced zoning), presumably in recognition of the fact that the need for supplementary bonding is now well understood.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.