Ring main extension for washer and dryer

[StuBeeDoo]

Good afternoon. I want to move our washing machine to a location away from the nearest point on the kitchen ring main, and at the same time include provision at the same location for a dryer - ie: alongside the washer.

My intention is to hard-wire both appliances, through separate switched FCUs. The appliances will be roughly a 10mtr cable-run from the point where I extend the ring-main (5mtrs there, 5mtrs back). I haven't checked, yet, but I assume the existing ring-main cabling to be 2.5mm2 twin and earth.

Would 2.5mm2 twin and earth be OK for a 10mtr run, bearing in mind the load washers and dryers require, or should I go up to 4.0mm2?

Thanks in advance,
Stuart.

 

[ericmark]

The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile from the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
(iv) taking account of the total floor area being served. (Historically, limit of 100 m² has been adopted.)

Reading that we should really have dedicated supplies for washing machine and tumble dryer, I know we don't, but where in the ring final we take high loads will make a difference.

In the main a washing machine (not washer/drier) takes high current for too short of a time to really worry about, so really looking at the tumble drier, I know our old vented type was 1 or 2 kW there was a switch to select, we always used the 1 kW setting, the new heat pump one not sure on how much power it uses, but unlike the element the heat pump does not run all the time, however as with any refrigeration device we are looking at volt drop, unless inverter controlled.

So start point is the readings, loop impedance at the consumer unit and loop impedance at the point you want to take a radial from will show the volt drop already existing and how close to centre of the ring final you are, the R1 + R2 readings will show how much cable already in the ring final, it is considered 106 meters to be the limit.

But without readings we are guessing, as an electrician I can make an informed guess, based on similar homes, but without seeing the home, I can't even guess how close already sailing to the wind, so can't really answer the question.

Any other method is trusting to the lord, and in the main we get away with it.

In my first house in the early 70's we washed in the kitchen, we dragged the twin tub to centre of the floor, and while washing, no cooking was done, the next house had a kitchen extension so the washing was done from a independent ring final and in the dinning area, so food and cloths did not really mix, and this house we have a utility room, so no cloths washed in the kitchen, and all the cooker was not in any way connected to the ring final in the kitchen, so no great load on it, this house ring split side to side of house, so loading of the two rings more even. Not worked out why rings ever split upper and lower seems an odd way to split.

So we can give pointers, but without readings your guess is as good as mine, likely better as you know the home.

 

[LeeJC]

What would be the point of using 4mm for a portion???
Your max current carrying capacity is going to be limited by your weakest link.
Assuming good ring continuity then your weakest link will be your MCB/RCBO (hopefully)............
FCU not a bad suggestion, but your protecting each accessory from overloading it's own connecting cable, unless of course you're intending to fit a greater than 32 Amp fuse in the FCU.............. Which I'd have to ask................ Why would you???

 

[ericmark]

What would be the point of using 4mm for a portion???

This was my question, without know the prospective short circuit current or the loop impedance how can we calculate volt drop or work out if the magnetic part of the MCB will operate?

Before adding to a ring final you need to know the readings so you can work this out. So without the instruments best option is the fused spur.

 

[EFLImpudence]

What would be the point of using 4mm for a portion???

It would save having to have two 2.5mm² cables in the same place.

 

[StuBeeDoo]

Thank you all for your contributions here.

Because I'm a bit OCD, my initial thought was to future-proof the job. But, as we have no intention of moving (thereby leaving our DIY for someone else's use) and we never have need to do more than one wash per day - meaning the washer and proposed dryer would never be in operation at the same time - you believe a 2.5mm2 fused spur off the kitchen ring should be adequate?

 

[EFLImpudence]

you believe a 2.5mm2 fused spur off the kitchen ring should be adequate?

I didn't mean that.

You either extend the ring - in which case you need two 2.5mm² cables running out and back in the same place, or

if you were to use use 4mm² cable then you would only need one cable to the sockets - and no fuse as the 4mm can handle >32A.

 

[Taylortwocities]

I often see this proposal to "spur" from a ring final using 4mm² cable. Ostensibly to provide a "high current" provision to another place.
Sometimes this extends to incorrectly providing what is effectively a sub-main to another consumer unit (garden shed/garage being the usual candidate).

In looking at the guidance on avoiding points of overload in the regs (Appendix 15), I can no examples where this can be allowed. Certainly I would not suggest it as a solution to the OP.

Extend the ring final in the proper manner. Two pieces of 2.5mm² cable. Thank you.

 

[EFLImpudence]

I often see this proposal to "spur" from a ring final using 4mm² cable. Ostensibly to provide a "high current" provision to another place.

It is not to 'provide' 'high current' [as it 'provides' (if that is the right word) no more current than the ring]; it is to negate the need for a fuse because the cable can carry the 32A of the circuit; the same as can the two 2.5mm² cables of the ring.

Sometimes this extends to incorrectly providing what is effectively a sub-main to another consumer unit (garden shed/garage being the usual candidate).

Why incorrectly?

In looking at the guidance on avoiding points of overload in the regs (Appendix 15), I can no examples where this can be allowed.

Please explain.

Certainly I would not suggest it as a solution to the OP.

Ok.

Extend the ring final in the proper manner. Two pieces of 2.5mm² cable. Thank you.

Do you men use 5mm² cable?

Might there be another way of connecting these two cables which are in the same place to the sockets?

 

[Taylortwocities]

Maybe I have misunderstood the purpose of a ring final

I always had thought that the principle was to distribute the loads around the circular cable arrangement. Avoiding single points of high load on the ring.

 

[EFLImpudence]

Maybe I have misunderstood the purpose of a ring final

I think you might have.

I always had thought that the principle was to distribute the loads around the circular cable arrangement. Avoiding single points of high load on the ring.

No, the 'principle' (is that the right word? Objective would be better) was to double the capacity of an existing 15A radial circuit while using the otherwise too small cable already in place because of a copper shortage after the war.

Another way (without that shortage) would have been to replace the 15A radial cable with a larger one (very large because of BS3036 fuses) that could carry the 30A - ring a bell?

 

[EFLImpudence]

In view of what you have written: when advising the extending of a ring circuit with cables out and back in the same place, do you advise that the additional sockets be only placed on side 'a' so that the ring shall be more balanced?

If not, then what is the difference?

 

[Taylortwocities]

I think you might have.


No, the 'principle' (is that the right word? Objective would be better) was to double the capacity of an existing 15A radial circuit while using the otherwise too small cable already in place because of a copper shortage after the war.

Another way (without that shortage) would have been to replace the 15A radial cable with a larger one (very large because of BS3036 fuses) that could carry the 30A - ring a bell?

Oh, you are much older than I thought. My Grandfather mention that wartime thing , indeed, that helped with materials shortages back then . But, and you know this, to use the smaller CSA copper the loads are evenly split across the two "half" of the ring. the amperage in each direction is shared allowing the use of wire with a smaller current-carrying capacity.
If you bang a 32amp (potential) load at a single point, there is nothing to stop Winston's wife from installing a Commando socket and plugging in a MIG welder,

 

[EFLImpudence]

Oh, you are much older than I thought. My Grandfather mention that wartime thing , indeed, that helped with materials shortages back then . But, and you know this, to use the smaller CSA copper the loads are evenly split across the two "half" of the ring. the amperage in each direction is shared allowing the use of wire with a smaller current-carrying capacity.

Yes, it is shared but not evenly.

Anyway, surely you are not advocating limiting the number of sockets on a ring to no more than three evenly spaced.

If you bang a 32amp (potential) load at a single point, there is nothing to stop Winston's wife from installing a Commando socket and plugging in a MIG welder,

There is nothing to stop her doing that on your extended ring.


Oh well, if that is the best you have...

 

[ericmark]

With the lolly pop design supplying for example a kitchen, there is no differential volt drop on the 4 mm² or 6 mm² cable so if for example you have a pair of double sockets as it leaves the cooker connection unit where it splits into the ring final, it can overload the short bit of cable connecting the sockets to the cooker connection unit, but if you use two 2.5 mm² cables in parallel and no 6 mm² cable from the CU to kitchen, then the resistance of the two 2.5 mm² cables well mean they better share the load, which is why any load for a reasonable time over 2 kW should be on its own dedicated circuit.

Kettle is OK as used for short time, and a washer without a drier again short time, I know from use of a narrow boat a 2 kW washing machine can run on a 6 amp B type MCB at 40ºC setting without tripping it as the time is so short. Even the oven does not take long to warm up, the problem equipment is:-

Immersion Heater
Tumble Drier
Range cooker

These may use less than 13 amp, but they use it for an extended time. And they are not classed as portable, so the appendix 15 suggests non portable over 2 kW should have a dedicated supply.

In the main we don't have a dedicated supply to the tumble drier, but as long as it is plugged in to a socket reasonably central to the ring final, it is not really a problem the MCB will trip before the overload causes damage. The problem with the lolly pop design is the drier may not be reasonably central.

There is nothing to stop us using our skill and extending a socket which is reasonably central to start with using a single length of 6 mm² instead of two lengths of 2.5 mm², but we clearly need to measure, easy using a loop impedance meter, we likely know the CU is 0.35 Ω and the donor socket is 0.62 Ω so likely a third of the way around the ring final, but the DIY guy likely does not have a loop impedance meter, maybe he does not need one, if the CU is 20 foot away then unlikely to be a problem, but if the CU is in the kitchen, then there may be a problem, but if in the kitchen easy enough to run a dedicated circuit.

The only problem is the Part P rules, but given the option do it safe or comply with Part P I would go for the safe method.

As to I am living in the house and I don't do XYZ well I never considered selling my last house until I retired, my father-in-law lived next door but one, when he died there were too many memories, so we moved, we had not planed on moving, but I could not remember what I had done in the house well before moving, when the ceiling was removed I looked up and said what are them wires for, I could not remember fitting them, but lived in the house from new.