Terminating Armoured cable for future use

[Jupiter01]

In addition to the "thanks" on your responses, I wanted to say thanks for all the info that many of you provide in response to my posts. There has been countless occasions where you have provided suggestions that I haven't even comprehended.

 

[JohnW2]

In addition to the "thanks" on your responses, I wanted to say thanks for all the info that many of you provide in response to my posts.

You're welcome (but see below).

There has been countless occasions where you have provided suggestions that I haven't even comprehended.

If you haven't comprehended the responses, you really should ask for further explanation/clarification, since that's the only way you will learn, and I'm sure that any of us would try to help further in that situation.

I'll take the opportunity to remind you, as I and others have said a number of times previously, that all the learning you are doing, with the aid of people here, about practical aspects and skills of electrical installations is all very well (and valuable to you), but you really do need to also gain a sound understanding of the more theoretical/'academic' underlying principles, by reading and/or attending 'courses', as a basis for your practical activities - and, as an extra bonus, once you have gained that understanding of the basics', learning other things (and practical skills) will become much easier.

Kind Regards, John

 

[SUNRAY]

I think we both misinterpreted/misunderstood. I didn't realise you were talking about an existing 'busy' CU - and was merely trying to say that it is much easier to make holes (for anything) before it is populated and wired.

Plastic CUs were/are sometimes rather flimsy (or otherwise not really suitable/ideal) for SWA glands, so it was not a bad idea to do much as you suggest, glanding the SWA into a small metal box which was right up against the CU, and taking the cores of the SWA (and it's 'inner sheathing') through into the CU - if he sees this bernard may well wheel out his standard photo of this!

You can still do the same with a metal CU, but it is then more possible that one could reasonably gland the SWA straight into the CU, hence not needing the box.

If, because the other end of the cable is not connected to anything (merely protected from water/moisture ingress), you don't want the cable energised at the moment, you don't have to connect the cores of the SWA to anything in the CU at this time - merely do something with them to 'make them safe'.

Kind Regards, John

I personally dislike an 'additional box', I see no point in introducing the additional work or cost of materials.

Having made that statement there may be situations where the CU and cable don't line up, for example:

This conduit couldn't be mounted any lower, if it were to be a SWA then an add on box would be the accepted solution.

 

[SUNRAY]

You're welcome (but see below).

If you haven't comprehended the responses, you really should ask for further explanation/clarification, since that's the only way you will learn, and I'm sure that any of us would try to help further in that situation.

I'll take the opportunity to remind you, as I and others have said a number of times previously, that all the learning you are doing, with the aid of people here, about practical aspects and skills of electrical installations is all very well (and valuable to you), but you really do need to also gain a sound understanding of the more theoretical/'academic' underlying principles, by reading and/or attending 'courses', as a basis for your practical activities - and, as an extra bonus, once you have gained that understanding of the basics', learning other things (and practical skills) will become much easier.

Kind Regards, John

Thaks John, I must add I'm getting more than a little nervous of the questions being asked. The sheer quantity of basics mixed with major subjects and now talk of doing works in others properties.
This is all getting way above the sort of advice we should really be giving.

 

[SUNRAY]

Deleted

 

[JohnW2]

I personally dislike an 'additional box', I see no point in introducing the additional work or cost of materials.

I agree that it's not very 'nice', but, for what it's worth (and presumably like bernard), I'm personally inclined to think that it might be the lesser of evils if the alternative is to attach an SWA gland to a flimsy plastic CU.

I have to admit that in my (very limited) experience, I have never taken SWA all the way to (or very close to) a CU, the transition from T+E to SWA (in some sort of 'box') always having been some appreciable distance from the CU. However, it is clear that, although I have not personally experienced them, there are plenty of situations (e.g. when it is to be buried, particularly if not RCD protected) in which it does need to be SWA all/most the way to the CU.

Kind Regards, John

 

[Jupiter01]

If you haven't comprehended the responses, you really should ask for further explanation/clarification, since that's the only way you will learn, and I'm sure that any of us would try to help further in that situation.

Sorry John. I meant to state that you guys provide me with suggestions that I haven't remotely considered prior to posting the question on this forum.
I am making my way through the on-site guide and hoping that was evident from this post

Cable and Breaker Sizes

I have been doing some reading on this topic and would welcome your comment/validation of the scenarios below please: 1. Oven Design current for this oven is 13 amp...

www.diynot.com

 

[Jupiter01]

I personally dislike an 'additional box', I see no point in introducing the additional work or cost of materials.

Having made that statement there may be situations where the CU and cable don't line up, for example:
View attachment 271633This conduit couldn't be mounted any lower, if it were to be a SWA then an add on box would be the accepted solution.

I presume this was necessary as the SWA could not be bent 90 degrees and glanded to the top of the CU?
Does the conduit going off to the left connect to an adaptable box where the gland is?

 

[EFLImpudence]

Here goes - from the linked thread.

I have been doing some reading on this topic and would welcome your comment/validation of the scenarios below please:

1. Oven
Design current for this oven is 13 amp

Plug it into a socket, then.

Therefore closest breaker size but higher than 13 amps is 16 amp. I will be using a 16 amp MCB

Yes.

which is within the protection range of the RCD

Don't know what that means.

Minimum cable size for this initially appears to be 2.5mm T&E based on reference method 103.

Don't use 103 then.
Minimum cable size for 13A is 1mm² T&E.

However, when I look at the voltage drop calculations and tables, I think this requires a minimum of 4mm T&E. This seems to be adequate up to a length of 66 metres. I have a 12 metre distance.

Haven't worked it out but if only 12m then will be different.

That said, I think the cable rating needs to be higher than the breaker rating? So, perhaps it needs to be 6mm T&E?

It does. Next higher than 13A is, as you say, 16A therefore 1.5mm² Method C will be adequate.

2. Lighting
Design current for the following is 0.634783 amps
24 4 Watt downlights
2 10 Watt bulbs
3 10 Watt external lights

Therefore closest breaker size but higher than 0.634783 amps is 3 amp. I think that's the lowest rating available? This is within the protection range of the RCD

Minimum cable size for this appears to be 1mm T&E based on reference method 103. I couldn't find anything in the voltage drop table for a 3 amp protective device. It starts at 6 amp. Why is that?

All irrelevant.
Don't install Method 103.
Voltage drop is not calculated by the MCB rating but the actual load and where it is on the circuit.
A 6A 1mm² circuit uses such an overated cable that you can ignore installation method (because 50% is the highest derating amount).
The voltage drop with LED lights is not worth working out.

Some specific questions please:
- I think my lighting scenario has quite a lot of lighting and yet it's not even an amp.

There you go.

Why are almost all lighting circuits protected at 6amps?

They just are because it is enough. Use 10A or 16A MCBs if you want.

- In scenario #2 if someone fitted a light which suddenly tipped the total current to 5amp, the 1mm cable is till good up to 8 amp but presumably the breaker will trip as soon as it exceeds 3 amps?

No, breakers never trip at 1.13 x In and take an hour at 1.45 x In. with differing times in between.

- Should cable rating always be higher than the fuse rating?

Generally yes but if the appliances cannot cause overload then not necessarily.

- I can understand how the MCB trips when the current is exceeded but what is the role of the MCB if a nail is hammered into the cable?

Because it causes a fault which generates lots of current. What do you think happens when you touch L & N or L & E together?
I can't believe you do not even know that.

I would welcome @Taylortwocities comments on this one.

So would I.

 

[JohnW2]

Thaks John, I must add I'm getting more than a little nervous of the questions being asked. The sheer quantity of basics mixed with major subjects and now talk of doing works in others properties. This is all getting way above the sort of advice we should really be giving.

I agree that it's a difficult, and fairly unique, situation.

In most senses, it is far from a case of someone 'fiddling about irresponsibly'. On the contrary, he seems almost obsessed with a desire to learn how to do things properly/safely, sometimes to the extent of being concerned about very 'trivial' (even if theoretically valid) details over which many/most would not loose any sleep. The only real issue, which several of us have pointed out to him, is that he is not really going about things 'in the right order', in that he needs to gain a good understanding of underlying electrical principles etc. before he starts try to learn about their practical application.

I, as a non-electrician, have to be careful about what I say, but I'm sure that it is (unfortunately) the case that some (practising') present day "electricians" have no more (maybe even less!) understanding of the theoretical 'basics' than does him. That does not 'justify' anything, but is an observation.

As for how we should react to this situation, some (perhaps partially including yourself) have seemingly decided that they don't feel comfortable 'getting involved', and I can understand that. Personally, I feel that it is very probable that he would continue doing (or trying to do) what he is doing, with or without input/assistance from anyone here (or elsewhere), such that to try to assist (whilst also repeatedly reminding him of the need to learn about 'the basics') is probably the lesser of the evils. In adopting that approach, I am somewhat reassured by the fact that he does seem to have a fairly good understanding of 'safe practices' whilst he is working.

However, as said, it's quite a 'difficult' situation.

Kind Regards, John

 

[EFLImpudence]

Error.

 

[JohnW2]

Error.

Not something that only happens with me, then

Kind Regards, John

 

[EFLImpudence]

Try again.


Worked out the Volt drop:
Edited - previously made a mistake with the cable sizes.

13A on 12m of 1mm² T&E is:

(22 + 22)mV x 13A x 12m / 1000 = 6.864V. Just over half of supposedly allowed limit.
(22 + 22)mV x 13A x 20m / 1000 = 11.440V


13A on 44m of 4mm² T&E is:

(5.5 + 14.5)mV x 13A x 44m / 1000 = 11.440V.

 

[Risteard]

Here goes - from the linked thread.


Plug it into a socket, then.


Yes.


Don't know what that means.


Don't use 103 then.
Minimum cable size for 13A is 1mm² T&E.


Haven't worked it out but if only 12m then will be different.


It does. Next higher than 13A is, as you say, 16A therefore 1.5mm² Method C will be adequate.


All irrelevant.
Don't install Method 103.
Voltage drop is not calculated by the MCB rating but the actual load and where it is on the circuit.
A 6A 1mm² circuit uses such an overated cable that you can ignore installation method (because 50% is the highest derating amount).
The voltage drop with LED lights is not worth working out.


There you go.


They just are because it is enough. Use 10A or 16A MCBs if you want.


No, breakers never trip at 1.13 x In and take an hour at 1.45 x In. with differing times in between.


Generally yes but if the appliances cannot cause overload then not necessarily.


Because it causes a fault which generates lots of current. What do you think happens when you touch L & N or L & E together?
I can't believe you do not even know that.


So would I.

Within one hour at 1.45 In - it varies between devices. No guarantee of operative between 1.13 and 1.45 times. They must not operate below 1.13 times and must operate within the conventional time (one hour) at 1.45 times. Nothing else should be read into it.

 

[JohnW2]

Within one hour at 1.45 In - it varies between devices. No guarantee of operative between 1.13 and 1.45 times. They must not operate below 1.13 times and must operate within the conventional time (one hour) at 1.45 times. Nothing else should be read into it.

All true, but not materially different from what EFLI wrote.