6mm cable for a hifi?

[HappyHippyDad]

Evening all.

A customer has asked for a dedicated radial circuit to feed 4 2g sockets.

He has asked for the cable to be rated at 45amps as he said at times the hifi equipment may reach this current. He is very specific that he wants the cable rated at this as a minimum.

He has asked for the 6mm to be terminated into an enclosure by the hifi which then feeds out in 2.5mm 'individually' to each of the sockets which are right by the enclosure (like an old spider circuit for lighting).

My plan was to use a 45A MCB for the circuit as the 2.5mm cable supplying the sockets will not need overload (O/L) protection and fault protection will be offered by the 30mA RCD (TT). Reference method will be 'C'.

I'd be interested in any opinions on this as it is a different style of circuit to 'normal' and those shown in appendix 15, but as stated fault protection is in place, O/L protection in place for the 6mm cable and protection against O/L can be omitted for the 2.5mm cable feeding the sockets (433.3.1 (ii)).

Cheers.

 

[amlu]

Evening all..

A customer has asked for a dedicated radial circuit to feed 4 2g sockets.

He has asked for the cable to be rated at 45amps as he said at times the hifi equipment may reach this current. He is very specific that he wants the cable rated at this as a minimum.

He has asked for the 6mm to be terminated into an enclosure by the hifi which then feeds out in 2.5mm 'individually' to each of the sockets which are right by the enclosure (like an old spider circuit for lighting).

My plan was to use a 45A MCB for the circuit as the sockets will not need overload (O/L) protection and fault protection will be offered by the 30mA RCD (TT). Reference method will be 'C'.

I'd be interested in any opinions on this as it is a different style of circuit to 'normal' and those shown in appendix 15, but as stated fault protection is in place, O/L protection in place for the 6mm cable and protection against O/L can be omitted for the sockets (433.3.1 (ii))?

looks like you have an "audiophile" customer. switch off the common sense, do whatever they want (but complying with the regs) if they want a 10mm cable feeding one socket why not. charge £££.

 

[Wonderwall]

What am I missing here?
Why does the 2.5mm cable not require protection?

 

[tazz]

Wow a 10kw audio amplifier.....where are your rewiring...Glastonbury...??/

 

[davesparks]

That has got to be one hell of a big house!
And isn't 45A on a 6mm pushing things a little bit assuming it's T&E, although if he is an audiophile it wouldn't be too hard to sell him 2H6 bare MICC polished with a super deoxygenate get sound enhancing polish (brasso)

As for the sound system, well, I know from experience that a small festival PA of around 20-25kW audio power will sit between 20A and 40A depending on the type of music and exact makeup of the stacks, and that'll keep a few thousand people happy in a field. so to pull 45A I'm guessing there's probably going to be something like 30kW of PA on the end of that.

 

[Octopus]

A customer has asked for a dedicated radial circuit to feed 4 2g sockets.



He has asked for the 6mm to be terminated into an enclosure by the hifi which then feeds out in 2.5mm 'individually' to each of the sockets which are right by the enclosure (like an old spider circuit for lighting).



Cheers.

So.... make the 6mm a sub main in SWA and in "his" enclosure mount a small CU with RCBO's


Or discuss the requirements again with the client as it does sound OTT

 

[Pete999]

Evening all.

A customer has asked for a dedicated radial circuit to feed 4 2g sockets.

He has asked for the cable to be rated at 45amps as he said at times the hifi equipment may reach this current. He is very specific that he wants the cable rated at this as a minimum.

He has asked for the 6mm to be terminated into an enclosure by the hifi which then feeds out in 2.5mm 'individually' to each of the sockets which are right by the enclosure (like an old spider circuit for lighting).

My plan was to use a 45A MCB for the circuit as the 2.5mm cable supplying the sockets will not need overload (O/L) protection and fault protection will be offered by the 30mA RCD (TT). Reference method will be 'C'.

I'd be interested in any opinions on this as it is a different style of circuit to 'normal' and those shown in appendix 15, but as stated fault protection is in place, O/L protection in place for the 6mm cable and protection against O/L can be omitted for the 2.5mm cable feeding the sockets (433.3.1 (ii)).

Cheers.

Just thinking you may have to question using 13 A sockets, or am I over thinking this?

 

[Lucien Nunes]

he said at times the hifi equipment may reach this current

For the first 20 milliseconds of inrush this might be true, but microwave ovens are the same and they don't need special circuits. If his system requires 45A during operation, his speakers will be on fire, or if it's transients he is worried about, he needs to get the reservoir capacitors in his amplifier changed.

Most HiFi woo collapses under engineering scrutiny. Where would all that power go? That's 10kW of heat it would be chucking out. A normal domestic system idles at maybe 20-50W input (listening audio power typically between 0.1 and 10W) and peaks at maybe a few hundred. OK, the power factor is typically low with a rectified load running well below maximum rating, so maybe that 200W requires 2A or so. Class A amplifiers consume their maximum power input at all times, wasting all that is not required for audio as heat. I use one of those, it requires 1.5A.

You can convincingly fill a large stadium on 45A. FWIW I used to be a live audio engineer and I've done it.

 

[Brightspark2]

What am I missing here?
Why does the 2.5mm cable not require protection?

It can't be overloaded. Have a look around the regulations mentioned in OP. There are other times where over Current protection is not required near the regulation.

 

[DPG]

Make sure you use oxygen-free and directional twin & earth cable. Or just draw some direction arrows on the normal stuff - he'll be well impressed.

Don't forget to have the local pylon and substation cables gold plated too.

Daz

 

[DPG]

There was a bit of a thing a few years ago for using 2.5mm twin and earth as speaker cable. Looks terrible though. Daz

 

[HappyHippyDad]

Thanks for the replies everyone.

He is more worried about 'transients' rather than the total audio power.

He's reading all sorts of things on line, speaking to the audio shop and changing his mind quite a bit. Originally he was going to go for oxygen free cable, but has decided against that. From what I read that is more about lengthening the lifespan of the cable rather than adding to any quality of sound.

Just this second had a text saying he wants an extra 2g socket! :biggrin:

 

[HappyHippyDad]

That has got to be one hell of a big house!
And isn't 45A on a 6mm pushing things a little bit assuming it's T&E, although if he is an audiophile it wouldn't be too hard to sell him 2H6 bare MICC polished with a super deoxygenate get sound enhancing polish (brasso)

As for the sound system, well, I know from experience that a small festival PA of around 20-25kW audio power will sit between 20A and 40A depending on the type of music and exact makeup of the stacks, and that'll keep a few thousand people happy in a field. so to pull 45A I'm guessing there's probably going to be something like 30kW of PA on the end of that.

Well it is really, but not for those reasons. It will be 6mm XLPE SWA thermosetting on outside wall, so CCC is 62A but T&E from the CU to outside wall (approx length 2m), this will be in trunking, so ref method B (sorry for not explaining this in OP). 10mm just seems complete overkill, but, if my breaker is 45A then I guess it's going to have to be 10mm from CU to outside wall as CCC is only 38A for 6mm T&E (table4D2A).

 

[davesparks]

Well it is really, but not for those reasons. It will be 6mm XLPE SWA thermosetting on outside wall, so CCC is 62A but T&E from the CU to outside wall (approx length 2m), this will be in trunking, so ref method B (sorry for not explaining this in OP). 10mm just seems complete overkill, but, if my breaker is 45A then I guess it's going to have to be 10mm from CU to outside wall as CCC is only 38A for 6mm T&E (table4D2A).

Why on earth are you putting 2m of T&E into the circuit if it's SWA? That's just adding an extra point of potential failure into the system and smacks of poor design.
Also you are using the wrong table for ccc of the SWA, it cannot carry 62A in this situation.

 

[HappyHippyDad]

Why on earth are you putting 2m of T&E into the circuit if it's SWA? That's just adding an extra point of potential failure into the system and smacks of poor design.
Also you are using the wrong table for ccc of the SWA, it cannot carry 62A in this situation.

The CU is inside (in a nicely decorated downstairs loo), it is plastic and I would not be able to terminate the SWA into it. I guess I could use 10mm for the whole run in conduit but I dont see a problem with a well terminated joint.

I am using table 4E4A for the XLPE SWA as it is 90c thermosetting clipped direct. I am using column 2, 2 core single phase as only 2 of the conductors will be carrying current and the 3rd used as the earth. I feel this is an ambiguous area, do you feel that it should be column 3 (3 core 3 phase, where you will have 3 live conductors each contributing to heat)?

You have asked 2 questions in this post, I have answered, if you feel the need to pursue them further then I'll try and accomadate for perhaps another post or 2 but If you feel able to offer your thoughts on which cable you would use... T&E/conduit, SWA etc etc based on the the facts above (tidy bathroom etc) that would be appreciated?