MCB Ratings for Storage Heaters

[Andelec]

I have recently had four storage heaters fitted by an electrician.

This is a completely new installation, including consumer unit and MCBs

There is one 3.3 kW storage heater, two 2.6 kW and one 1.7 kW

The four MCBs for the storage heaters are each rated at 20 amps

Is that correct for the above storage heaters?

I would have expected one 10 amp and three 16 amp MCBs

What is an expert's view on this please?

 

[SPECIAL LOCATION]

Circuit breakers are to protect cable not the load..

e.g.

providing all of you cables can safely carry 20amps.. such as 2.5mm Twin & Earth..

then 20A MCBS are fine..

You could consider it similar to the road speed rating of the tyres on your car...

you may well find your tyres are rated for up to 140+MPH..

e.g.

Speed Ratings - Tyre Speeds Explained | Blackcircles.com

But you car can only just reach 95MPH

So as long as the MCB and Cables can supply the full load the is likely to be drawn all is good!

you would only need to worry if the cables rated less than 20A.. say 1.5mm T&E!!

:coffee

 

[PC Electrics]

All sounds good to me.

---------- Post Auto-Merged at 11:22 ---------- Previous post was made at 11:19 ----------

You don't say what size cable is used. What size does the certificate quote? 2.5mm probably.

The only thing I'd might have done differently would be to use 16A MCBs and 1.5mm cable on the smaller heaters. Purely to keep material costs down.

 

[Andelec]

Thank you for your advice.

Yes, it is 2.5mm cable on all the storage heaters.

I do appreciate that MCBs are there to protect the cable, but what about the appliance?

Do they not play a part in protecting that also?

If so, why not err on the side of caution and fit an MCB closer to the rating of the appliance?

 

[PC Electrics]

What 'protection' do you envisage the appliances need that isn't provided by the MCBs?

The appliances are fixed load, so cannot overload the circuit.

In the case of a short circuit inside an appliance the MCB will trip as required.

You have no need to worry. All is as it should be.

 

[Manator]

All the heaters will be connected via a fused spur outlet which will have a fuse rating according to the manufacturers instructions. If you plug any appliance into your socket circuit it is likely that the circuit is 32amp, but your appliance will have a 3,5, or 13amp fuse fitted to the plug.

 

[Andelec]

Fused spur outlet?

To clarify, do you mean that the on/off wall switch for the storage heater should have a pull out cartridge fuse on the front of it?

In this case, none of them do.

 

[Manator]

If the manufacturer has stated a fuse rating for the heater it will be connected via a fused spur. It is possible that it is wired through a double pole switch rated at 20amps, this would look like a normal light switch on the outside.

As others have posted above the rating for the cable is covered by the 20amp mcb's, as they are fixed loading, they are not likely to draw more than the cables rating factor.

 

[Andelec]

They are double pole 20 amp double pole switches and I wouldn't have thought a fused spur for a 3.3 kW storage heater would be suitable anyway.

Thanks for all your help, I just needed clarification on this.

 

[SPECIAL LOCATION]

Thank you for your advice.Yes, it is 2.5mm cable on all the storage heaters.

I do appreciate that MCBs are there to protect the cable, but what about the appliance?

Do they not play a part in protecting that also?

If so, why not err on the side of caution and fit an MCB closer to the rating of the appliance?

NO the MCB's are not there to protect appliances..

Electric showers, cookers, immersion heaters don't have fuses..

If an appliance needs fusing the manufacture will have installed that inside the device or request it be connected via a fused spur connection.

What if multiple heaters were to be installed onto one circuit?

You do not design circuit by just picking MCBs for the load..

You pick the correct cable for the max load

Then the correct MCB for the cable

Allowing for things like

Instillation methods and routing of cables

and nuisance tripping of devices due to power on surges

etc...

The more likely problem that the appliance will have is going open circuit and drawing NOTHING!

i.e. it will most likely have its own internal trip devices thermal and/or overload...

The actual cost of a 20A / 16A / 10A will typically be the same if they are made by the same manufacture!

So there is NO valid reason for fitting individual ratted MCB's

In fact it is easier for the installer just to have to carry ONE size of MCB & the single cable size than have a varied selection of MCB's!

 

[sparkytim]

FCU on the larger storage heaters NOT a good idea

Have replaced many burnt out 13 Amp fused connection units just not up to 3.4 Kwatt load over long durations.

Just another tip, try and not wire 3.4 Kwatt loads from adjacent Mcbs, have found normal Heat generated in MCB can trip them, try and leave a blank space between or mix heater sizes

 

[Manator]

13 amp should be good up to 3.2, but I would doubt I would put one on anything larger. Like you say its pushing the limits really.