Shower dims house lights

[geordie]

Been out to look at a shower which when it is switched on dims the lights in the house. Shower is 8.5Kw wired in 6mm on a 32a breaker.cable installed behind plasterboard Voltage drops from 240 to 233 when switched on. Now I believe that the shower installed in this way should be on 10mm cable. And this would help stop the big drop in voltage.

 

[Coffeemad]

according to my maths 8.5KW = 36.96amps. Sounds like a new shower on an existing cable, installed by the homeowner

 

[malcolmsanford]

The unit would pull roughly 35.4 amps at 240v which most showers are rated for, but as with all these units you will find that it will run lower than that.

If what you say your dropping 7 volts that is still well within the 11v or 5% allowed for volt drop.

I think though you are right that 10mm and a 40amp breaker would have been better for this, has that 32amp is working to the limit when the unit is first switched on, though I suspect because of the limited use the breaker gets it will be quite happy.

I would be looking more towards a loose connection for the lights dimming. Try checking the connections of the tails at the CU and the meter. Check also the lighting circuit connections see if you have loose connections, you can check the connections by doing a R1+R2, if you get an higher than expected result then you may have a loose connection.

 

[Rockingit]

If another circuit is exhibiting signs of voltage loss though, I'd be looking upstream at connections in the CU and size of tails.

 

[MarkieSparkie]

Because the heavy load of the shower on the installation is causing the voltage to drop sufficiently to dim the house lights on a separate circuit(s), this points to the problem (most likely one or more loose connections) being upstream, including all the common elements of the installation to these circuits e.g. Terminal Bars and Blocks, RCD, Main Switch, Meter, Supply Isolator, DNO Fused Head, e.t.c.

 

[oldtimer]

Plumbers are the worst culprits with these thing ie 6mm supply 7Kw shower and they chuck a 8.5 or even 9.0Kw and the reasons why they do not get caught out is that these showers are running at 60% FLC also if there is a rewirable 3036 fuse then happy days as for the lights dimming a guy I knew got a 10.5Kw shower put in and yes the lights dimmed when switched on and I advised him that he should not run any other heavy appliances in the house whilst having a shower because he only had a 60A main fuse .

Lets face it I dont have an electric shower I have a power or pumped shower plus a hot water tank but I do not know anyone who has a good word to say about instant electric showers the manufacturers are making them bigger load wise and we are running even bigger cables to satisfy the demand.

 

[Rockingit]

Must admit, I put a 10.5kW one in at my house when I rewired, and I can't really see an appreciable difference to the 8.5kW it replaced, other than watching how fast the meter blinks!! Oh, and all the GU10's dim ever so slightly, too, and my connections are all torxed-tight.

 

[DPG]

I wouldn't be without an electric shower. I've known quite a few people who have been stuck when the boiler packs in and they can't have a bath or shower till parts arrive for boiler!

I've got a 10kW Gainsborough copy (Sadia) which never needs to be run anywhere near its full load (stays on 'medium' setting, and is quite happy on a 40A MCB. Daz

 

[Knobhead]

If the lights are dimming then the voltage is dropping at the CU, volt drop at the shower is a separate problem. Get your meter on the CU bars and see what drop you are getting with the shower on. It could be a DNO problem in which case god help you because I doubt they will or simply a poor connection on the tails, isolator or RCD.

 

[seb77]

is the shower breaker nearest to the main 100a main switch?. ive had lights dim when the 6amp lighting breaker is nearer to the main switch.Instead of the biggest mcb nearest the main switch some clown had done the smallest 1st and biggest furthest away. changed them round and bingo.

 

[c.boy]

If you were to test the incoming supply, you will prob find that the voltage reading you get will be around 230-235 volts!!!!!so you aint getting a volt drop at all!!!!!We are meant to be on a 230v supply after all!!

 

[telectrix]

turn off lights before taking shower. problem sol-ved.

 

[Rockingit]

is the shower breaker nearest to the main 100a main switch?. ive had lights dim when the 6amp lighting breaker is nearer to the main switch.Instead of the biggest mcb nearest the main switch some clown had done the smallest 1st and biggest furthest away. changed them round and bingo.

given the rating of solid copper bus bars it's more likely it was a loose connection that got tightened when you did the work!

 

[Rockingit]

If you were to test the incoming supply, you will prob find that the voltage reading you get will be around 230-235 volts!!!!!so you aint getting a volt drop at all!!!!!We are meant to be on a 230v supply after all!!

Voltage drop is measured from the point of origin, not assumed (though calculated for design) and takes into account the whole installation. That's why it's given as a percentage figure, not a hard figure. Most houses down here see 245v, but you still have to design around 230v.

 

[cdavies33]

This is a DNO problem! 100% I have the same problem where I live, the most likely fault is a faulty joint under ground, We had the DNO out redone the joint and sorted. It only took about a year to get them out tho!!!!


Good luck to your customer...... They are gonna need it.