Electric shower causes light to dim

[Sinful]

Hello,

When we turn the electric shower on (10.5kW) it causes any filament type lamps in the house to dim. I've measured the voltage at one of the sockets and when the shower is turned on it drops by approximately 10V.

Do I have a problem? I've done a search on the forum and there are a few similar posts but the opinions on whether this is normal or not seem to conflict.

I've checked the connections at the CU Main switch and they seem fine, any advise would be much appreciated.

 

[westie101]

Any additional load will cause voltage to drop, in a lot of cases it depends on the type of supply (overhead or underground) the distance to the substation, the size of the cables in between, even the load on the network
What does it drop from and to?
Do you see a smaller drop when the kettle is switched on?
Do you see a "dip" when the hoover is switched on?

But yes if there are no signs of problems around the CU, meter and cut-out it would be normal.

 

[Sinful]

Any additional load will cause voltage to drop, in a lot of cases it depends on the type of supply (overhead or underground) the distance to the substation, the size of the cables in between, even the load on the network
What does it drop from and to?
Do you see a smaller drop when the kettle is switched on?
Do you see a "dip" when the hoover is switched on?

But yes if there are no signs of problems around the CU, meter and cut-out it would be normal.

Hi there,

At time of testing shower took me from 245V down to 235V. Just tried the kettle and it gives a proportional 2V (approx) drop.

Not tried the Hoover, will have to get the missus to show me how it works!

It's an underground supply btw.

Cheers

 

[westie101]

Unless it gets worse I wouldn't worry about it

 

[Sinful]

Unless it gets worse I wouldn't worry about it

Thanks, will stop obsessing now

 

[ban-all-sheds]

I have a 10.8kW shower.

I don't notice anything dropping/dimming when I turn it on.

Unless it gets worse I wouldn't worry about it

If he is seeng a 10V drop when he draws 44A then that implies a 230mΩ resistance between the cutout and the CU incomer. I would not be as blase as you about that. 10V & 44A mean 440W being dissipated somewhere - easily enough to start a fire.

 

[ebee]

10v does sound excessive.
Most installations will have a brief light dim under such a load.
Mostly noticeable if you are looking away from the light - ie an illuminated wall - with filament lights.

I`d get someone qualified to check connections, cable size and volt drop if I were you..

You might have a dodgy incommer

 

[viewer]

To the OP :
Of those making replies. there is one qualified and experienced professional person who is currently working in exactly the right field to give you an expert opinion.

 

[Johnmelad]

To the OP :
Of those making replies. there is one qualified and experienced professional person who is currently working in exactly the right field to give you an expert opinion.

What a wonderful informative reply you gave. I am sure it helped the OP no end.

 

[Sinful]

I have a 10.8kW shower.

I don't notice anything dropping/dimming when I turn it on.

If he is seeng a 10V drop when he draws 44A then that implies a 230mΩ resistance between the cutout and the CU incomer. I would not be as blase as you about that. 10V & 44A mean 440W being dissipated somewhere - easily enough to start a fire.

Thanks for replying.

Would the resistance not be between the origin of the supply and the CU incomer rather than just between the cutout and the CU incomer?

I must say that the tails going into the CU do look poor, they have been oversleeved with heat shrink but from what I can see look like very old cloth covered wiring. Unfortunately the meter is sealed so I can't check the meter connections, everything in the CU is tight though.

 

[viewer]

"If he is seeng a 10V drop when he draws 44A then that implies a 230mΩ resistance between the cutout and the CU incomer"

Surely that would only be true if the voltage at the cutout did not vary?

Westie's reply suggests that it is likely to vary as the complete supply system needs consideration.

 

[ebee]

To the OP :
Of those making replies. there is one qualified and experienced professional person who is currently working in exactly the right field to give you an expert opinion.

There could be more than one

 

[DetlefSchmitz]

Can we put the question like this? What is the range of typical mains input impedances expected in a UK domestic supply?

 

[viewer]

To the OP :
Of those making replies. there is one qualified and experienced professional person who is currently working in exactly the right field to give you an expert opinion.

There could be more than one

Yep. Apologies. I read the posts when I got up. There were only two replies at the time (about 5). I started to write and then got taken off to deal with something else. When I came back a couple of hours later I finished and posted without checking whether there had been posts during that period.
PM to ebee, but not sure it worked.

 

[ebee]

No it didn`t work. I think you gotta be friends first.