Quote from: Scrumpy on May 18, 2023, 09:36:10 AMBeautiful morning.. 

Alex.. You could put it up in bunches..

I was  booked in for highlights Scrump, I need to lighten my mood     

Nice sunny day in North Lincolnshire.

I'm waiting for a couple of 40 amp MCBs to arrive so I can make our consumer unit shower circuits comply with the wiring regulations.

Both showers are rated at 8.5 kW but are connected to 50amp MCBs which is a big no no as the regs state that the MCB should be the nearest rating to the amperage in the circuit.

8.5 kW at 230 volts gives 37 amps (rounded) so the maximum MCB is 40 amps.

The other concern, which I'll rectify, is that should both showers be activated at the same time there would be a 74 amp load, in addition to any other loads, on a DNO fuse rated at 80 amps which could, potentially, blow.

The installer should have provided a load sharing facility which I will do.

This demonstrates that the Part P regulations, which allow electricians to pay a few quid to a regulatory body & then self-certify their own dodgy installations are not for purpose IMO.

So will you be following the regulations and not doing the fitting yourself?

Quote from: klondike on May 18, 2023, 09:52:08 AMSo will you be following the regulations and not doing the fitting yourself?

I can change the MCBs as under Part P it's one of the jobs that's not notifiable.

A friend has an old consumer unit with no RCD protection so I'm replacing the MCBs with RCBOs.

I had a lengthy conversation with our local Building Control Officer & he also confirmed it wasn't a notifiable job but asked me to ensure that the RCBOs were compatible with the consumer unit so I got all the necessary information from Wylex.

I have advised my friend that he needs at least a new consumer unit at some point in the not too distant future.

This is where the Part P regs are a bit sloppy as it's allowable to repair or extend an existing circuit but not to install a new circuit so installing a load sharing device isn't installing a new circuit, it's modifying two existing circuits.

However, I have asked a neighbour, who is Part P registered to install it as & when I get the necessary device.

He hadn't heard of what I want doing so I've sent him details of what it is & how it has to be installed.

Just checked and mines on a 50A breaker too. I changed the shower on it and don't recall what it was originally but the one I fitted is 9kw. My only concern in selecting it was that it wouldn't exceed the breaker capacity.

Quote from: klondike on May 18, 2023, 12:38:26 PMJust checked and mines on a 50A breaker too. I changed the shower on it and don't recall what it was originally but the one I fitted is 9kw. My only concern in selecting it was that it wouldn't exceed the breaker capacity.

A 9 kW shower will pull 39 amps (rounded) at 230 volts & the regs say that the MCB should be the nearest rating to the load, which in your case would be a 40 amp MCB.

Also your shower cable should be 10 mm.

However, provided your shower cable is 10mm & not 6mm, your 50 amp MCB should be ok.

I would estimate that at least 75% of electrical fires are caused by a mismatch of cable size & MCB rating.

Another thing I found with our consumer unit was that screws hadn't been tightened to the correct torque settings so I spent a good amount of time slackening them all off & then re-tightening them with my torque screwdriver, so something else the Part P guy didn't do.

Loose connections that cause arcing are also a cause of many house fires.

https://bit.ly/3BD2nkx

There is a dusky fellow in the woodpile when cutting the numbers that tight though.

The mains voltage here isn't 230v it is higher (the meter is correct as it tallies with my multimeter).



If my shower is indeed rated at 9,000w at 230v that puts its resistance at 5.9 ohms and it will draw 42 amps at 247 volts (all approximate).

That said looking at the specs they do say 230v + 10% and a 40A supply which means that 9kw rating is the highest it can use and it will be lower on most supplies.

Quote from: klondike on May 18, 2023, 07:23:03 PMThere is a dusky fellow in the woodpile when cutting the numbers that tight though.

The mains voltage here isn't 230v it is higher (the meter is correct as it tallies with my multimeter).

If my shower is indeed rated at 9,000w at 230v that puts its resistance at 5.9 ohms and it will draw 42 amps at 247 volts (all approximate).

That said looking at the specs they do say 230v + 10% and a 40A supply which means that 9kw rating is the highest it can use and it will be lower on most supplies.

The leeway for 230 volts is between -6% & +10% but if your voltage is normally 247 volts your 9 kW shower will pull 36.44 amps.

Our mains voltage is actually 237.9 volts so our 8.5 kW showers will each only pull 37.83 amps which is why the 50 amp MCBs had to go.

The IET 18th Edition regs, to the best of my knowledge, stipulate that 230 volts must be used for all single phase domestic electrical calculations, which why I base mine on 230 volts.

I think 240 volts can be use in a domestic 3 phase system but I'll have to check.

The regulations are changing rapidly & all new consumer units have to be metal & at some point not too far away it will be mandatory to have surge protection & RCD / RCBO + AFDD circuit breakers in all consumer units, not just in some high risk premises where they are already mandatory.

And snap, I've got a very similar power monitor, slightly different case but same function buttons.

The resistance of the element is fixed not the power produced so an increase in voltage will lead to both increased power and current. From the specs of mine I assume that the 9kw will only get produced when it runs on 230 + 10% or 253 volts and lower voltages will use less power.

The voltage isn't fixed here or I presume anywhere. It is currently 244.6v. There can be minor variations in frequency  too but they don't show on that as it only gives whole numbers. They do show on my multimeter though.

Could we do with an electrical section  ?    

cleaning lady this morning, practice nurse this afternoon for odd dry patches of skin which are appearing - it's all go!

Morning, Pool at 7am,then coffee from the wee flask while watching the ocean. Walk for Dageus then see what needs doing round here, might have a bit of a sleep after lunch see how I feel.

sounds good!

Quote from: Alex on May 18, 2023, 11:14:06 PMCould we do with an electrical section  ?    

I suppose it could but it started off in the correct thread as I was saying what I was doing that day, as per the title of the thread.

Perhaps we have a volunteer to moderate the threads. We might be getting a spanking.