Dedicated mains - Survey

James,

You could well be right - but it’s one hell of an assumption to make. If you were to put such an argument to any electrician or to the Fire Service I’m sure the response would be rather robust and certainly unprintable here.

Phil,

I must confess I’ve done similar things in the distant past. Even, and I’m truly ashamed to admit it, wired across the fuse holder with copper wire, which as I said earlier is truly insane. And it was at my parents’ house too. I shudder when I think of what could have happened. But yes it does sound better with less fuses - no question. I’m a lot older now and no longer possess the confidence / recklessness of youth. Thank God!

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It’s not an assumption. The device itself has a fuse in the IEC socket, which will protect the device from overload / fault current and so the fuse in the plug only has to deal with a catastrophic event such as a short circuit on the cable. I don’t have the relevant BS number to hand, but i very much doubt Naim are playing fast and loose here with plug fuse ratings as they will have had to conform to various standards to obtain certification of their products.

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James,

I take your point and I did wonder about the equipment fuse. I also can’t imagine that Naim would be foolish enough to break any regs. That’s what set me wondering about the whole thing. Still I’m not convinced that it would cut much ice with any official bodies like the fire service or with say an insurance investigation.

It still amounts to fitting an incorrectly rated plug fuse with respect to the cable. At the end of the day that’s the bottom line and I think it would be viewed in a very bad light, even if it is not actually illegal. In the final analysis it’s doing something incorrect in order to improve sound quality. I can’t imagine this ever being done with any equipment other than hi-fi because there would be zero point in it. That in itself says something.

Ok Pete. I don’t see an issue with it.

I’d suggest that if you think Naim have got it wrong with their interpretation of the relevant standards with regards to the plug fuse rating, you contact them and ask them to clarify their choice.

I’ll leave it there.

James

I don’t know about the UK but I can’t imagine that it’s worse than the EU with regard to certification and such. Every device sold here must have a CE certification and so on, and they have the stickers on the back and declarations in the manual. Else they would not be in stores. In any case, I would think Naim know what to do, you are worrying about nothing

On the box of the Powerline Lite, it just says use an appropriate fuse to match the appliance, but it does not give a maximum current rating. Of course some people might use this cable to power up a multi-socket block, which could equate to >6amps continuous, or possibly used in a Graham Hydra, or in fact used for anything with an IEC Socket, such as a kettle maybe.

However, after saying that, Naim will have taken the spec for the cable from it’s makers, not from some generic worst case scenario table. If you actually do the full cable calcs yourself and apply every derate component accurately you’ll probably find you get a very different answer! For example, not all conductors and Insulation are the same. Piro cable for example can be much thinner for extremely high loads because of its construction. So I think we are all safe, but a good question none the less.

I’m not suggesting that. I am saying this:

FACT: The fuse fitted to the plug is inadequate to protect the cable.

This makes it a safety compromise in the name of sound quality regardless of any other considerations.

If you see my previous response, then I think all we can say is:
FACT: The fuse fitted to the plug is inadequate to protect a standard 0.75mm off-the-shelf flex/cable

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GadgetMan,

Not sure what you are getting at here. Are you suggesting that the construction of the cable is such that the current rating capabilities of the 0.75mmsq conductors are modified so that they are now able to handle over twice their normal rating? Seems highly unlikely to me. Moreover my understanding is that the standard Naim lead is simply a generic cable that was selected from many after extensive listening tests. Nothing special about it.

I’m saying it’s a possibility, without knowing the makeup of that cable, we cannot say what’s its specifications are. For example, if it were pure silver, then again the spec would be different. Also the insulation could be different, for example the insulation on the flex that is used to feed an immersion heater, has to be different to a standard flex in order to run under the higher heat conditions.

A 1mm Piro cable can handle 18amps, but a 1mm standard flex can only handle 10amps - same diameter, but different cable makeup

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Well an immersion heater flex as you say has to have heat resistant insulation for obvious reasons. But this insulation has no bearing on the current capacity of the cable. That is dictated by the conductor cross-sectional area.

Pyro cable is a special case whereby the conductors are insulated by copper sheathing and mineral material which means that they are able to continue to carry current at very high temperatures without breaking down or without them causing fires. In other words they are both resistant to the external heat from a fire and also to their own conductors over-heating and causing a fire in the event of the current exceeding the normal conductor rating.

In your example of a 1mmsq Pyro cable. The conductor rating is still the same - 10A. The reason the Pyro cable can handle 18A is simply because although the conductors will be dangerously over-heating at this level by dint of the cables very tough insulation it will not cause a fire.

No. There is no cable construction on earth that will increase the standard current rating of the conductors. Reduce it yes - but increase it, no way.

I tried to find the spec of the cable, and came across the link below which seems to match my Powerline lite:
Here it defines the current as “(under 50ft long) 10 amps”, so this would indicate a 0.75mmsq cable can run at higher currents and still meet a whole bunch of certificates. Clearly though, it does say 13amps

Hi GadgetMan,

Sorry but again I’m unsure what you are getting at.

The Powerline Lite is just the standard Naim power lead fitted with a Powerline plug and as you say is 0.75mmsq.

The current ratings for conductor CSA are as follows:

0.75mmsq. 6A

1mmsq. 10A

1.5mmsq. 16A

The Powerline Lite is rated at 6A and therefore fitting the plug with a 13A fuse will not adequately protect the cable.

Apologies if I am not getting across what I think I am.

What I am saying is that the 6 amp limit for 0.75mm flex is just a guideline, to be used where no other detail is available.

The actual current carrying capacity of cables varies depending on lots of criteria. These are defined in the Regs (appendix 4) as Reference methods A/B/C/D, so for example a 1mm multicore thermoplastic insulated cable (single phase) has a limit of 11 amps when enclosed in conduit in thermally insulated wall, but has a 17 amp limit when in free air.

That same diameter cable but with thermosetting insulation (e.g. immersion heater) is 14.5 amps when enclosed in conduit in thermally insulated wall, but has a 21 amp limit when in free air.

So current carrying capacity of a given diameter varies depending on the insulation type and how it is used.

In the powerline lite cable, we know the specification of the 0.75mm flex used is 10amps according to the manufacturer, so that would be a more accurate figure to use than that standard tables.

Just my view of course, and as I said, doesn’t explain why the fuse is 13 amps.

GadgetMan,

Yes I see now what you are saying. I’m not familiar with the figures you are quoting but they appear to be at odds with every spec I’ve ever seen, ie. you are saying that a 1mmsq cable has a 17A limit rather than 10A. This makes no sense to me.

Yes the current rating of a cable can certainly be reduced in certain circumstances. The figures I have quoted for current capacity are for cables under normal circumstances, ie. not enclosed in conduit or tightly coiled etc. In other words the same circumstances that a Powerline Light would be used in.

The Powerline Light is just a ‘normal’ cable. Nothing special about it at all, except that it has been chosen from many different such cables as sounding the best of the bunch. I can’t understand how it can possibly be rated at 10A as that is the rating for a 1mmsq cable. If that’s what the manufacturer says then presumably it’s correct but it makes no sense. But in that case the plug should be fitted with a 10A fuse not 13A, so we’re back to where we started!

Perhaps somebody with a greater knowledge could shed some light on this?

Pete

Maybe, if this issue is so important to you, you can start a thread on it.

Jim

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My existing wiring is in good condition and is about 35 years old … and run as ring circuits… I don’t use internal dedicated wiring for my audio systems… but do use dedicated external wiring audio extension cabling… which is an EMI / RFI resisting braided multi copper strand format…
Have changed sockets to Crabtree unstitched sockets for main Hi-Fi connection to appropriate ring.

However the main thing I have done to improve SQ (and other significant non Hi-Fi benefits) is convert my house earthing from TNC grounding system to a TT grounding system. Now that has been worthwhile, certainly in a small village distribution mains feed setup.

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Not really so important to me Jim, I don’t actually own any Naim electronics now. Rather just puzzled and curious to get to the bottom of what seems to be - on the face of it - a contradiction and which possibly could have wider implications. However I accept this thread probably isn’t the right place so apologies for the diversion and let’s move on.

I can imagine. This likely got rid of a lot of earth pollution and other nasties (for SQ).

TT is the most widely used system worldwide I believe.