Fitted Electric Shower - now lights dimming

[eng_tech_solutions]

An Electric Shower has been fitted - 10.5kW, 10.0mm2 cable, 40A MCB, RCD protected. When the Electric Shower is switched ON the lights dim.

The voltage when the shower is OFF measures 235V. When the shower is turned ON the voltage drops down to 222V. Obviously, more than 4% drop so does not meet regs.

The suppliers fuse is 60/80A. The manual reccomends 80/100A.

The suppliers quoted £370 to upgrade the fuse to 100A + 8/10 week waiting time but will the fuse upgrade fix the problem? Does the cable coming into the house need to upgraded as well? Cant see how upgrading the fuse will fix the problem..... Help appreciated.

 

[JohnD]

The fuse change is oddly expensive. A fuse will not help. The voltage drop is due to cable size. If they are going to upgrade your supply cable that would help, but not often needed. Your meter tails will also want to be 25mm but this is a very short length so unlikely to be the cause.

Are you in a converted or very old property or a long way from the road? Is it an undergound or overhead supply?

Can you put up a pic of your electrical installation (incl meter, fuse, consumer unit) which may give some clues?

 

[sm1thson]

how long is the cable running from the CU to the shower?
-i am assuming from the large drop the voltage was measured at the shower end? -or was it measured at the CU end? (hence the lights dimming)

 

[Steve]

Lights dimming is nothing unusual. Switch your kettle on, you'll notice the same happens then, obviously not as harshly.

10.5kw is 45.6A at 230v, so you need a 45 or 50A MCB.

 

[Adam_151]

10.5kw is 45.6A at 230v, so you need a 45 or 50A MCB.

But his shower will be rated at 240v (i've never seen one that isn't), which gives you 43.75A, it'll say on the line below in brackets something like "(9.6kw @ 230v)" so infact his shower will only take 41.74A on a 230v supply

So you can use a 45A breaker without worrying about breaking the reg by 600ma

@OP... whats the PSCC?

(btw, 4% only applies to your cabling, we don't sutract the DNOs drop from this)

 

[eng_tech_solutions]

Thansk for the reply -

The voltage measured (235V downto 222V) is at the CU 100A isolator since I wanted to check what is happening to the primary supply.

25mm2 tails are used which are less than 1m long from the meter. All neatural and live connections have been double-checked.