Hmm that's very much not correct! The light switch needs changing for an FCU (Fused connection unit) with a 3/5amp fuse for the light. I wouldn't advise having the same 'electrician' back if he's incapable of carrying out such a simple job correctly.
Electrical work?
- Thread starter morpheus83uk
- Start date
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I agree that, if we are understanding correctly, the electrician obviously should not have done it, but it seems that the OP may have at least partially brought this on himself, by asking the electrician to replace the FCU with a switch! ....
Kind Regards, John
Or pay for someone to do it properly.
Re your last post (how apt)
I hope you mean MCB, not RCD?
And you MUST limit the current on the boiler to no more than 3 amps
And you must limit the current on the lighting circuit to no more than 6amps - assuming the lighting wiring has been done in 1mm² conductors
I need some education here. Some/many would say that one should 'limit the current' to 6A because of the 'ratings' of accessories, but why are you implying that a 1mm² cable requires a 6A 'limit'?
Kind Regards, John
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I am trying to simplify the issues for the DIYer. There are no signs of him getting the 'electrician' or anyone to sort this out for him.
Yes i know that 1mm² is capable of more than 6amps, but we don't really know what the CSA is of any of the wiring. So, I am trying to have him err on the side of caution.
The feed is apparently from a B16 "RCD"
Yes i know that 1mm² is capable of more than 6amps, but we don't really know what the CSA is of any of the wiring. So, I am trying to have him err on the side of caution.
The feed is apparently from a B16 "RCD"
Yes, I realised that, which is why I wondered why you seemed to 'unsimplify' the situation by adding "... assuming the lighting wiring has been done in 1mm² conductors" to what was otherwise adequate and simple advice
Indeed so - but we're used to that one!The feed is apparently from a B16 "RCD"
Kind Regards, John
Morpheus83uk, you seem to be getting confused between a RCD and a MCB. They are different devices and NOT the same.
MCB's will have a letter being either B,C,D followed by a number being either 3,6,10,16,20,32,40, 45,50, or 63. The number refers to how many amps the circuit is rated for, think of it like a 3 vs 13 amp fuse in the plug - Higher number for higher powered circuits. (i.e. B16 refers to a type B MCB rated for 16 amps.)
MCB's will normally only take 1 space up in the consumer unit.
RCD's on the other hand are devices that protect against residual current leaking through earth - They are the same type of device you might plug into a electric lawn mower for example to reduce the chance of a fatal electric shock should a electrical fault occur. (i.e. you mow over the wire.)
RCD's will normally take 2 spaces up in the consumer unit.
By your description, it sounds like your boiler and light are both on the same 16 amp type B MCB. If this is the case, the light needs to be on a switched FCU with a 3 or 5 amp fuse in, and the boiler on a swithed FCU with a 3 amp fuse in.
Just to clarify, you need two switched fused spur units (one for the light and one for the boiler) what operate independently of one and other.[/quote]
MCB's will have a letter being either B,C,D followed by a number being either 3,6,10,16,20,32,40, 45,50, or 63. The number refers to how many amps the circuit is rated for, think of it like a 3 vs 13 amp fuse in the plug - Higher number for higher powered circuits. (i.e. B16 refers to a type B MCB rated for 16 amps.)
MCB's will normally only take 1 space up in the consumer unit.
RCD's on the other hand are devices that protect against residual current leaking through earth - They are the same type of device you might plug into a electric lawn mower for example to reduce the chance of a fatal electric shock should a electrical fault occur. (i.e. you mow over the wire.)
RCD's will normally take 2 spaces up in the consumer unit.
By your description, it sounds like your boiler and light are both on the same 16 amp type B MCB. If this is the case, the light needs to be on a switched FCU with a 3 or 5 amp fuse in, and the boiler on a swithed FCU with a 3 amp fuse in.
Just to clarify, you need two switched fused spur units (one for the light and one for the boiler) what operate independently of one and other.[/quote]
Ok thank you or the explanation and help so far.
The B16 is on the MCB NOT the RCD.
I would like to clarify what I asked of the electrician. I asked if the switch in the cupboard could be changed from a fused switch to a normal switch and he said it would be fine because the correct cables were being used. So lighting cable going to the light and I assume normal socket cable going to the MCB (but this is speculation based on what he told me). So with this information I was told by a qualified person it was fine to do if it wasn't fine to do and needed to stay there I wouldn't have minded it was more a question for aesthetics than anything else.
So from what I can gather the power comes in from somewhere and then is sent to the boiler from the 1st floor of the house to the garage (why it was not moved to the garage MCB's when the boiler moved there I don't know).
The Boiler has a fused switch above it which has a 3A fuse in it where the power comes in so as far as I am aware this is the FCU. So that part I believe from what I have read is fine the only thing which is wrong (bar the wiring) is that its should be a B6 MCB opposed to a B16?
As for sorting the wiring so I dont need to keep the light switch on would I be best (based on what is being said) to have a 2 gang 2 way switch one of which has power coming in for it and the boiler on it which is switches on all the time. Then bridge the power to the other socket and have this as the light switch or would this still be wrong and I have misunderstood?
Or is it that I need to change it back to a fused switch with a 3A and then this would work fine for both of them or would it still need to change the B16 at the MCB?
Thanks
James
The B16 is on the MCB NOT the RCD.
I would like to clarify what I asked of the electrician. I asked if the switch in the cupboard could be changed from a fused switch to a normal switch and he said it would be fine because the correct cables were being used. So lighting cable going to the light and I assume normal socket cable going to the MCB (but this is speculation based on what he told me). So with this information I was told by a qualified person it was fine to do if it wasn't fine to do and needed to stay there I wouldn't have minded it was more a question for aesthetics than anything else.
So from what I can gather the power comes in from somewhere and then is sent to the boiler from the 1st floor of the house to the garage (why it was not moved to the garage MCB's when the boiler moved there I don't know).
The Boiler has a fused switch above it which has a 3A fuse in it where the power comes in so as far as I am aware this is the FCU. So that part I believe from what I have read is fine the only thing which is wrong (bar the wiring) is that its should be a B6 MCB opposed to a B16?
As for sorting the wiring so I dont need to keep the light switch on would I be best (based on what is being said) to have a 2 gang 2 way switch one of which has power coming in for it and the boiler on it which is switches on all the time. Then bridge the power to the other socket and have this as the light switch or would this still be wrong and I have misunderstood?
Or is it that I need to change it back to a fused switch with a 3A and then this would work fine for both of them or would it still need to change the B16 at the MCB?
Thanks
James
Sorry just had a thought it could be wrong but I thought I would put it out there...
I have had another look at the cables behind the switch and I have sorted out the original issue so the switch works fine now and the boiler stays on all the time. On closer inspection I have 2 2.5mm cables coming in from the MCB and going to the boiler and the other cable is 1.5mm going to the light.
As the 2.5mm cable can take more amps than the 1.5mm if the amps exceeded 15 amps (I believe this is what 1.5mm cable is rated at) then the cable could catch fire but the other cabling would be fine as it is designed to take this and the MCB would not trip as it is not exceeding 16 amps.
So If I were to use a fused switch and had a 3A fuse in it and had the boiler and the feed in coming into the load live and then just the light on the switch if anything greater than 3A came from the feed the fuse would blow causing no damage to the lighting cable... If this then travelled down the cable towards the boiler the 3A fuse would blow there as well protecting the boiler.
Would this work and if so is it correct and safe? Or is this what someone has already said and I am just repeating this?
From the previous post I have re read it sounded like I was required to have two separate fused switches one for the boiler and another for the light however would this not do the same thing as there are still two fuses in play one each for the boiler and the light? Obviously still the 16A at the MCB too.
Thanks
James
I have had another look at the cables behind the switch and I have sorted out the original issue so the switch works fine now and the boiler stays on all the time. On closer inspection I have 2 2.5mm cables coming in from the MCB and going to the boiler and the other cable is 1.5mm going to the light.
As the 2.5mm cable can take more amps than the 1.5mm if the amps exceeded 15 amps (I believe this is what 1.5mm cable is rated at) then the cable could catch fire but the other cabling would be fine as it is designed to take this and the MCB would not trip as it is not exceeding 16 amps.
So If I were to use a fused switch and had a 3A fuse in it and had the boiler and the feed in coming into the load live and then just the light on the switch if anything greater than 3A came from the feed the fuse would blow causing no damage to the lighting cable... If this then travelled down the cable towards the boiler the 3A fuse would blow there as well protecting the boiler.
Would this work and if so is it correct and safe? Or is this what someone has already said and I am just repeating this?
From the previous post I have re read it sounded like I was required to have two separate fused switches one for the boiler and another for the light however would this not do the same thing as there are still two fuses in play one each for the boiler and the light? Obviously still the 16A at the MCB too.
Thanks
James
That is not clear but I think I know what you mean.
Exceeding 15A and less than 16A will not trip nor set light to anything .
That is correct but current does not 'come from' the feed; it is drawn by the loads.
Les than 1A by the boiler and even less by the light.
Yes, sounds good.
Probably.
Yes, it would but isn't that was what you were saying?
Thank you for that sorry it took a while I just wanted to make sure I had it in my head correctly.
I will go out and swap the face for a fused switch tomorrow hopefully and then get it sorted at weekend.
I do have one question though if the current exceeds 15A and is less than 16A would the wire for the light (rated at 15A) not melt like in a fuse?
Thank you for all your help.
James
I will go out and swap the face for a fused switch tomorrow hopefully and then get it sorted at weekend.
I do have one question though if the current exceeds 15A and is less than 16A would the wire for the light (rated at 15A) not melt like in a fuse?
Thank you for all your help.
James
No. Apart from there being generous safety margins (although these should not be considered in design work) it does not work like that.
Anything rated at 15A will not vapourise at 15.1.
Take an MCB rated at 16A.
These must carry 1.13 times this rating for ever - not trip.
1.45 times for an hour before tripping.
Over this and the time gets progressively quicker until
5 times the rating in 0.1 seconds.
Fuses are even more tolerant of overload.
Obviously the cable can cope with this without damage.
Ah right its just I thought that it would be like a fuse which is why it was unsafe and could potentially start a fire. It makes sense to build in margins for safety. I always thought that anything past the fuse or MCB's load will cause it to trip straight off so anything more than 16A for example will cause it to trip.
Also I have heard of electrical tests which are done to test the speed of the RCD and this is done by sending a fault current? How does this work?
Thanks Again
James
Also I have heard of electrical tests which are done to test the speed of the RCD and this is done by sending a fault current? How does this work?
Thanks Again
James
Thank you for the link so basically any leakage in current round the circuit will trip the RCD to ensure the circuit is not live and to stop electrocution.
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