Can fused spurs be put in series

13 Feb 2005
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United Kingdom

I am going to get an electrician in to make the connections for electric underfloor heating I am installing in my bathroom. There is already a heated towel rail installed that is powered from a fused spur in the bedroom.

Would it be OK to take the power from this fused spur to another one that can then be used to feed the thermostat/matting for the underfloor heating.
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Wiring in series is not the right terminology, but I understand what you are asking.

Physically this is fine to have two loads of a spur providing it is a fused socket as you suggest you are using. However, you will have an issue with the total load.

As the spur is 13A then you only have a maximum load 2990 watts. (13A x 230V)

I imagine that a towel radiator will take use of this wattage up. You will have to add the power of the towel radiator and underfloor heating together. If greater than 2990W then a separate spur will be needed. Have a look in the specifications of your appliances
Agree, need more information on loads.
One point. The underfloor heating MUST be protected by and RCD. Does the circuit you are going to use have an RCD.
If not then the fused spur for the floor heating should be a 30mA RCD

If you are doing the wiring, has your electrician advised you of the requirements for equipotential bonding. You will need to do this before you tile etc otherwise you'll have earth wires hanging about the place.
The basic rule for safe wiring is: the fuse must be small enough to protect ALL the wiring that comes from it and the wires need to be thick enough to support the load, subtracting the correction applying to where and how the cables are run, which sometimes can double the required csa. As this becomes a rather technical story, suffice it to say that your question is not as simple to answer as you might expect.
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Thanks for the replies. The underfloor heating is only 200w and the heated towel rail is 150w so no problem with loading. Although I don't think you quite get what I mean. I am going to have 2 fused switched outlets but I would like to take the live and neutral from the 1st one (before it passes through the fuse i.e Input) and pass this to another fused spur, this would save me having to lift flooring to break into the ringmain to run the L/N to the second fuse spur.

The consumer unit is protected by a 30mA RCD would this satisfy the requirements for the ring being on an RCD.
Your total load is less than 3A. you could run both from the one FCU but you'll need two FCUs if you want to switch them off independently.

IF the existing FCU is on the RING you could spur off that to the new FCU for the UFH.
The first FCU is spured off the ring, is it OK to have another FCU spured off the 1st one because I would like the switch each on/off independently.
No you cant. that is a spur off a spur.
You would need to include both FCUs in the ring. If you are not sure, you are better off getting your electrician to do this for you.
No problem I'll put the first FCU onto the ring and then spur off that.

With regard to the underfloor heating being protected by an RCD will the fact that all my ring mains for power sockets are protected by an RCD 30mA at the consumer unit or will I have to get an RCCB fitted for the ring main that feeds the underfloor heating.
You do not need another RCD if the ring that will feed the UFH is already protected by the 30mA RCD in your consumer unit.
Whilst you can't spur off a spur you could have two FCU off the first FCU. This would allow you to independently switch the towel rail and the underfloor heating. Not pretty but it works - and complies.

The total power for both circuits will be limited by the fuse in the first FCU.

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