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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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    Put them on 40 A final circuits. And do it with the three-phase board: better balance, less copper, room for two more, altogether neater, and maximum 80 A per phase. 


    The only reason I could see for wanting higher-rated circuits would be if an upgrade to e.g. 10.5 kW showers is considered, or the "9 kW" showers are really rated 9.6 kW and the designer insists on working with I = 9.6 kW / 230 V (in the days of 240 V it would have been just ok). 


    Perhaps (thinking of another thread recently, about ovens) the shower manufacturer would even require a lower protection rating than 60 A. 


    Try this example of an installation manual (manufacturer:pdf,  archived:pdf)  - see the top of page 7, where it sensibly declares 40 A as ok for the 9.5 kW rating. This implies that the power rating is at 240 V, and given that when fully on it's basically a resistor, a 230 V supply will take even less current.  It doesn't say "must be connected to a 40 A MCB, no more and no less": but I feel that connecting to 63 A would be harder to justify. 

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    Put them on 40 A final circuits. And do it with the three-phase board: better balance, less copper, room for two more, altogether neater, and maximum 80 A per phase. 


    The only reason I could see for wanting higher-rated circuits would be if an upgrade to e.g. 10.5 kW showers is considered, or the "9 kW" showers are really rated 9.6 kW and the designer insists on working with I = 9.6 kW / 230 V (in the days of 240 V it would have been just ok). 


    Perhaps (thinking of another thread recently, about ovens) the shower manufacturer would even require a lower protection rating than 60 A. 


    Try this example of an installation manual (manufacturer:pdf,  archived:pdf)  - see the top of page 7, where it sensibly declares 40 A as ok for the 9.5 kW rating. This implies that the power rating is at 240 V, and given that when fully on it's basically a resistor, a 230 V supply will take even less current.  It doesn't say "must be connected to a 40 A MCB, no more and no less": but I feel that connecting to 63 A would be harder to justify. 

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