Regulation 434.2.1- would this comply?

[Mr Carl]

People,
First post as new to the industry and the forum. Would like thoughts on wether members would consider the following scenario would comply with regs, particularly 434.2.1.
Bathroom in a 2 story detached house is being renovated. An electric shower is being removed from the bathroom which was fed from the consumer unit on 6mm t+e from 40A type B MCB. The 6mm cable running in the loft space.
The new bathroom will now contain a mixer shower to which a pump situated in the airing cupboard will be fitted. This shower will be over a whirlpool bath.
My thoughts are to replace the 40A MCB with a 16A mcb. Run the 6mm into a junction box in the attic directly above the airing cupboard. Run two 1.5mm cables from junction box, through the plasterboard ceiling into the airing cupboard where they will be clipped direct into switched FCU's, 5A for shower pump and 3A for the bath.
The 1.5mm cable in the loft space does not pass through insulation.
I have taken the ambient temp in the loft to be 40 degrees requiring an It of no less than 18.4A.
My concern would be that someone throws loft insulation over the short run of 1.5mm cable in the attic in the future further derating the current carrying capacity of the cable.
In that scenario, the cable is still effectively protected by the fuses in the FCU's downstream.
My question is therefore that in that scenario does the wiring comply with reg 434.2.1.? The run of 1.5mm from junction box to FCU being less than 3m.
Thanks.

 

[Bob Geldoff1234]

I would personally be running 2 x 2.5mm t&e down to the switched FCU's and then spur off those with your 3 or 5 amp fuses.Make sure they have 30ma RCD protection protecting the 6mm.

 

[telectrix]

to be safe, extend the 6mm (using a MF wagobox) to the 1st FCU in the airing cupboard. this will eliminate problems caused by the itchy-poo monkeys in the attic.

 

[Bob Geldoff1234]

Have fun trying to get a 6mm and 2.5mm into the spur

 

[Wilko]

Have fun trying to get a 6mm and 2.5mm into the spur

Should go into the terminals, but it could be "pig wrestling in the pattress"

 

[Mr Carl]

Thanks. The circuit is protected by a 30mA RCD at the cu. Out of curiosity, why not use 1.5mm cable if the ccc is 18.4A when allowing the derating due to the higher ambient temp and the MCB is rated at 16A?
Does reg 434.2.1 not mean that the MCB is protecting the 6mm cable, with the downstream fuses effectively protecting the respective 1.5mm branches or am I missing something?

 

[Wilko]

Just looking at clipped direct 1.5mm its 20A at 30C from Table 4D5 and from Table 4B1 Ca is 0.87 for 40C giving 17.4A. But if it was 50C up there (which I bet it is today) it'd be 14.2A. Using 2.5mm, its 27A, 23.5A and 19A, so all would be well. If the 2.5 got covered by <100mm itchy it'd be 21A, 18A and 14.9A, which is not good in the worst case (that doesn't exist now). That said, I wouldn't use 1.5 for a power circuit in a loft

 

[Pete999]

People,
First post as new to the industry and the forum. Would like thoughts on wether members would consider the following scenario would comply with regs, particularly 434.2.1.
Bathroom in a 2 story detached house is being renovated. An electric shower is being removed from the bathroom which was fed from the consumer unit on 6mm t+e from 40A type B MCB. The 6mm cable running in the loft space.
The new bathroom will now contain a mixer shower to which a pump situated in the airing cupboard will be fitted. This shower will be over a whirlpool bath.
My thoughts are to replace the 40A MCB with a 16A mcb. Run the 6mm into a junction box in the attic directly above the airing cupboard. Run two 1.5mm cables from junction box, through the plasterboard ceiling into the airing cupboard where they will be clipped direct into switched FCU's, 5A for shower pump and 3A for the bath.
The 1.5mm cable in the loft space does not pass through insulation.
I have taken the ambient temp in the loft to be 40 degrees requiring an It of no less than 18.4A.
My concern would be that someone throws loft insulation over the short run of 1.5mm cable in the attic in the future further derating the current carrying capacity of the cable.
In that scenario, the cable is still effectively protected by the fuses in the FCU's downstream.
My question is therefore that in that scenario does the wiring comply with reg 434.2.1.? The run of 1.5mm from junction box to FCU being less than 3m.
Thanks.

Take the 6mm into the airing cupboard, terminate into a dual accessory box fit 2 FCUs and wire in suitably sized cables for your 2 supplies, derate the breaker to a 20 Amp

 

[Mr Carl]

Just looking at clipped direct 1.5mm its 20A at 30C from Table 4D5 and from Table 4B1 Ca is 0.87 for 40C giving 17.4A. But if it was 50C up there (which I bet it is today) it'd be 14.2A. Using 2.5mm, its 27A, 23.5A and 19A, so all would be well. If the 2.5 got covered by <100mm itchy it'd be 21A, 18A and 14.9A, which is not good in the worst case (that doesn't exist now). That said, I wouldn't use 1.5 for a power circuit in a loft

Take your point about the higher temp. However at 40C with In being 16A, then the cable would need to be capable of carrying 18.4A Using equation 1 page 333 of the regs.
Point I'm wrestling with is, under normal conditions the 1.5mm cables will be pulling less than the 3 or 5A depending on the branch. Well within the current carrying capacity even with temp of 50C.
Under fault conditions at the load then the fuses will protect the cables of each branch. With that in mind would this set up comply with reg 434.2.1?
"A device for protection against fault current may be installed other than at the point where a reduction in the cross sectional area or other change causes a reduction in the current carrying capacity of the conductors under the following conditions
In the part of the conductor between the point of reduction of csa or other change and the position of the protective device there shall be no branch circuits or socket-outlets and that part of the conductor shall:
(i) not exceed 3m in length
(ii) be installed in such a manner as to reduce the risk of a fault to a minimum
(iii) be installed in such a manner as to reduce to a minimum the risk of fire or danger to persons.

 

[Ian1981]

As long a

People,
First post as new to the industry and the forum. Would like thoughts on wether members would consider the following scenario would comply with regs, particularly 434.2.1.
Bathroom in a 2 story detached house is being renovated. An electric shower is being removed from the bathroom which was fed from the consumer unit on 6mm t+e from 40A type B MCB. The 6mm cable running in the loft space.
The new bathroom will now contain a mixer shower to which a pump situated in the airing cupboard will be fitted. This shower will be over a whirlpool bath.
My thoughts are to replace the 40A MCB with a 16A mcb. Run the 6mm into a junction box in the attic directly above the airing cupboard. Run two 1.5mm cables from junction box, through the plasterboard ceiling into the airing cupboard where they will be clipped direct into switched FCU's, 5A for shower pump and 3A for the bath.
The 1.5mm cable in the loft space does not pass through insulation.
I have taken the ambient temp in the loft to be 40 degrees requiring an It of no less than 18.4A.
My concern would be that someone throws loft insulation over the short run of 1.5mm cable in the attic in the future further derating the current carrying capacity of the cable.
In that scenario, the cable is still effectively protected by the fuses in the FCU's downstream.
My question is therefore that in that scenario does the wiring comply with reg 434.2.1.? The run of 1.5mm from junction box to FCU being less than 3m.
Thanks.

In a nutshell the fault protection and overload can be on the load side of the supply where a reduction in CSA, ccc occurs and 3 meters is max length stated before being fused down as it where.

 

[Mr Carl]

Thanks Ian1981. I take it you think it does that scenario would comply then?

 

[davesparks]

The regulation also requires that the cables not liable to faults or damage, or words to that effect. So unless you are going to put them in steel conduit or similar then you can't really apply the rules about protection after the reduction in CSA.

With regards to the use of 2.5mm for this circuit, the main reason I know of is that it is traditionally the size of T&E used for 16A and 20A radials in domestics. Plus the majority of electricians working in domestic usually don't carry 1.5mm on the van as standard.

 

[Wilko]

Hi - if you are changing to a 16A mcb and the cable used after the 6mm can be protected by that mcb, then aren't we ok? This is what Reg 434.2.2 refers to, I think.

 

[davesparks]

As long a

In a nutshell the fault protection and overload can be on the load side of the supply where a reduction in CSA, ccc occurs and 3 meters is max length stated before being fused down as it where.

You've missed out conditions (ii) and (iii) to that regulation. The risk of fault must be reduced to a minimum and the cable must be installed in such a manner as to reduce the risk of fire or danger to persons.

T&E on its own does not have enough mechanical protection to reduce the risk of fault to a minimum.

 

[Ian1981]

You've missed out conditions (ii) and (iii) to that regulation. The risk of fault must be reduced to a minimum and the cable must be installed in such a manner as to reduce the risk of fire or danger to persons.

T&E on its own does not have enough mechanical protection to reduce the risk of fault to a minimum.

You've missed out conditions (ii) and (iii) to that regulation. The risk of fault must be reduced to a minimum and the cable must be installed in such a manner as to reduce the risk of fire or danger to persons.

T&E on its own does not have enough mechanical protection to reduce the risk of fault to a minimum.

the op listed the 3 conditions before I posted so why repeat what he'd already posted

 

[davesparks]

the op listed the 3 conditions before I posted so why repeat what he'd already posted

I don't mean that you should repeat what has been posted, but that your post makes it appear that length is the only consideration and that you are agreeing that it can be applied here without further consideration.

 

[Ian1981]

I don't mean that you should repeat what has been posted, but that your post makes it appear that length is the only consideration and that you are agreeing that it can be applied here without further consideration.

Fair enough