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electric showers

Former Community Member
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Hello again, following on from the recent topic that discussed sizing electrical supplies to fixed equipment we have been asked to install 4 number 9KW electric showers into the same commercial premises as my earlier question on RCD protection to lighting.

Designer has asked for a 250A SPN sub board, (3 phase supply is available) and 4 x 60A SPN supplies to the showers with 60A DP isolators. When I checked the model MI they state a 40A supply is required. I queried this with the designer and his answer is that the showers draw 39A so wants the 60A supplies. Apart from the fact I can't find a decorative DP switch rated at 60A, am I missing something in that this feels unnecessary. No cable sizes have been discussed yet, 

Showers are on an office floor with 200 or so desks so assuming similar numbers of staff although not convinced that all staff will be lining up to use the showers on a daily basis. 

Again thanks in advance for any thoughts.
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    No harm in over specifying the shower isolators, and arguably a good idea if remembering the failure rate of fully loaded shower switches. I would consider a rotary switch that can be padlocked off for safe maintenance.

    The OCPD should however be correctly rated according to the instructions with the shower, probably 40 or 45 amps.

    Electric showers can result in earth leakage currents, and it would be preferable in my view NOT to add showers to any existing RCD, for fear of total leakage currents tripping an RCD. Use a dedicated RCBO for each shower.


    Do double check that enough power is available to add a load of about 80 amps to one phase, and 40 amps to the other phases.

    Most office showers see relatively little use, but the installation should not rely on this. Heavy and repeated use is certainly possible. I recall an unfortunate episode during the great Dartford power failure some years ago.

    A multi tenanted office building had a 315 amp 3 phase service. The electric showers added by each tenant added up to about 500 amps per phase, not normally a problem with limited use of each shower.

    Due to the general power cut in the area, which did NOT affect this building, there was a queue for showers. The cut out fuses operated, repeatedly.
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    No harm in over specifying the shower isolators, and arguably a good idea if remembering the failure rate of fully loaded shower switches. I would consider a rotary switch that can be padlocked off for safe maintenance.

    The OCPD should however be correctly rated according to the instructions with the shower, probably 40 or 45 amps.

    Electric showers can result in earth leakage currents, and it would be preferable in my view NOT to add showers to any existing RCD, for fear of total leakage currents tripping an RCD. Use a dedicated RCBO for each shower.


    Do double check that enough power is available to add a load of about 80 amps to one phase, and 40 amps to the other phases.

    Most office showers see relatively little use, but the installation should not rely on this. Heavy and repeated use is certainly possible. I recall an unfortunate episode during the great Dartford power failure some years ago.

    A multi tenanted office building had a 315 amp 3 phase service. The electric showers added by each tenant added up to about 500 amps per phase, not normally a problem with limited use of each shower.

    Due to the general power cut in the area, which did NOT affect this building, there was a queue for showers. The cut out fuses operated, repeatedly.
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