Hi all, Ok heres the problem. My brother has just bought a newly built house, it has an electric shower in the en-suite which is a 9kW shower. The main bathroom has no shower but he would like to install one, but I think adding another electric shower (say 9kW for this example) would be overloading the consumer unit. Looking at the consumer unit it is a split load board with a 100 amp main switch & a 63amp RCD. The individual circuits on the board are protected via MCBs. The meter tails supplying the consumer unit are 25mm & the company fuse is marked 60 amp The main switch section of the consumer unit supplies: The ground floor lights- The 1st floor lights- The smoke alarms- The boiler The RCD part of the consumer unit currently supplies: Shower- Electric cooker- Ground floor ring main- 1st floor ring main The new shower would be connected to the RCD section of the consumer unit. I think this would be over loading the RCD & maybe the whole board & could be dangerous. For example: If both showers happened to be on that would be a load of 18 kWs (18000 watts) 18000 / 240 = 75 amps. There would also be the load of the rest of the circuits. I know that there are calculations that are applied to certain electrical appliances /circuits to take into account that all items connected wont be switched on at the same time (diversity calculations) but I dont know how these work & if they are applicable to the Consumer unit. I thought it best to ask advice as maybe someone out there has faced a simular situation. Any advice on this topic would be greatly appreciated. Regards, TB

Tel boy wrote | I think adding another electric shower (say 9kW for this example) | would be overloading the consumer unit. | Looking at the consumer unit it is a split load board with a 100 amp | main switch & a 63amp RCD. The individual circuits on the board are | protected via MCBs. | The meter tails supplying the consumer unit are | 25mm & the company fuse is marked 60 amp 25mm is normal but a 60A main fuse is very low these days. Ask supplier if it can be upgraded. | The RCD part of the consumer unit currently supplies: | Shower- Electric cooker- Ground floor ring main- 1st floor ring main | The new shower would be connected to the RCD section of the consumer | unit. | I think this would be over loading the RCD & maybe the whole board & | could be dangerous. I wouldn't be happy having 2 x 45A shower circuits on one 60A RCD. If there is space in the CU you could put the second shower on the non-RCD side of the CU, using an RCBO which is a combined MCB and RCD for that circuit. They usually take the space of 2 MCBs Owain

| I think adding another electric shower (say 9kW for this example) | would be overloading the consumer unit. | Looking at the consumer unit it is a split load board with a 100 amp | main switch & a 63amp RCD. The individual circuits on the board are | protected via MCBs. | The meter tails supplying the consumer unit are | 25mm & the company fuse is marked 60 amp 25mm is normal but a 60A main fuse is very low these days. Ask supplier if it can be upgraded. | The RCD part of the consumer unit currently supplies: | Shower- Electric cooker- Ground floor ring main- 1st floor ring main | The new shower would be connected to the RCD section of the consumer | unit. | I think this would be over loading the RCD & maybe the whole board & | could be dangerous. I wouldn't be happy having 2 x 45A shower circuits on one 60A RCD. If there is space in the CU you could put the second shower on the non-RCD side of the CU, using an RCBO which is a combined MCB and RCD for that circuit. They usually take the space of 2 MCBs Just a thought, but if you're resigned to a bit of plumbing and a lot of electrics (the new cable to the new shower is going to be a *pig* to run, believe me), is there any reason why you shouldn't install a pumped shower instead? Even one of the cheap all-in-one units should match the electric shower for flowrate and the electrics will be simplified greatly - you will just need to take a fused spur from the upstairs ring. You may need to install a Surrey Flange (I think that's what they're called) in the tank, but there seem to be a lot of people on this ng who get by quite nicely without one. I suppose if the hot water isn't stored there might be a problem but... well, it's a thought. Hwyl! M.

| The RCD part of the consumer unit currently supplies: | Shower- Electric cooker- Ground floor ring main- 1st floor ring main | The new shower would be connected to the RCD section of the consumer | unit. I wouldn't be happy having 2 x 45A shower circuits on one 60A RCD. More to the point, why are the shower and the cooker on the RCD side in the first place?  It's a new supply, so presumably PME.  Assuming the protection is a Type B MCB and the cable is 10mm^2, there's no earthly (excuse pun) reason for the shower to be RCD protected. (Circuit length is limited by voltage drop, not earth fault loop impedance.)  Consider moving cooker and shower(s) to the non-RCD side (carry out earth fault loop impedance tests after doing this).   The present arrangements are not compliant with the current On-Site Guide recommendations, which say that an RCD installed to protect sockets (for portable equipment outdoors) should protect only those sockets.  It's a poor show if this has been specified for new house building.