Are 16 mm meter tails good for 99A?

[Harry Worth]

Sorry folks if this topic is done to death. I've just been working with a spark who's put 16mm tails on a 100A fuse. I queried this and he responded with 'I'll show you in the regs - It's OK'. I've since tried to find the relevant table. Looking at table 4D1A - it gives 87A current carrying capacity for single core 70 degree thermoplastic clipped direct. Is this the correct table? The table doesn't show values for cables spaced or in free air. The tails in this instance are separated, short and not directly clipped to wall at some points. My question - does this mean the actual capacity can be taken as higher than 87A as the conditions are better than those in this table? If i take the 25mm table the capacity increases from 114A (ref method C) to 130A for spaced by 1 diameter. If I apply this factor to 16mm cable it suggests the cable is good for 99A (appreciate the calc's a bit rough and ready - I've probably ignored a square law). The house doesn't have an electric shower etc so current peaks are probably well within the 87A in any event.

 

[trev]

Is that 87A diversified?

 

[Harry Worth]

Is that 87A diversified?

- That's the figure from the regs that's quoted as the actual current carrying capacity of the cable (if I'm using the right table that is). So no, I'm not considering diversification just the protection of the 16mm tails with a 100A fuse.

 

[trev]

Sorry Harry I thought you meant your total load is 87A. If the total load after diversity is below this then right now you'd be ok with 16mm tails, but (it's a big but) what's to say that next week they're not going to go out and buy a megawatt shower?
I'd stick 25s in as a matter of course but that's just me

 

[Octopus]

Without a power shower the average house isn't going to pull much over 50A (if that) so I wouldn't loose any sleep over 16mm tails.

 

[kingeri]

There must be many, many houses out there with 16mm tails and 100a main fuse. It's not ideal, and I'd replace with 25mm if it's convenient to do so, but as Murdoch says, it's nothing to fret about. I certainly wouldn't go breaking seals etc. In the case the OP is on about, I'd have installed 25mm no question.

 

[Geordie Spark]

Without a power shower the average house isn't going to pull much over 50A (if that) so I wouldn't loose any sleep over 16mm tails.

How much extra do you think a "Power Shower" will add to the load ??

 

[telectrix]

think he meant instantaneous shower. anyway, i posted some time ago where a pub kitchen was pulling 90+A through 16mm and i measured the cable temp. after 45mins. ( that's when the 63A breaker tripped) and it had just got to 39deg., well short of the max. 70deg. so i also would not lose any sleep over it. obviously, from a design stage, you'd fit 25mm.

 

[Geordie Spark]

think he meant instantaneous shower. anyway, i posted some time ago where a pub kitchen was pulling 90+A through 16mm and i measured the cable temp. after 45mins. ( that's when the 63A breaker tripped) and it had just got to 39deg., well short of the max. 70deg. so i also would not lose any sleep over it. obviously, from a design stage, you'd fit 25mm.

I do too ..... I was just being a pedantic sod

 

[DNG]

Would anyone consider using 16mm tri-rated cable as apposed to 25mm for a 100A cable head

 

[telectrix]

have done so. need to ferrule the ends though.

 

[Octopus]

How much extra do you think a "Power Shower" will add to the load ??

An INSTANTANEOUS shower load would depend on the rating!!


lol

 

[Geordie Spark]

An INSTANTANEOUS shower load would depend on the rating!!


lol

Good lad !! :yes::clap:

 

[zzzzzz]

What size are the cables from the main fuse to the feed side of the meter? Are they 16mm? If so changing the load side tails only upgrades part of the installation,albeit the feed tails are the DNOs baby.
I worked for a DNO for a long time,and after fitting 16mm tails off an 100a main fuse since time began,one day it dawned on someone 16mm was rated about 97a so we then started fusing down to 80a.
I would fit 25mm as someone else has said, but I wouldn't lose a great deal of sleep over this either way.
Just a thought-have you actually checked the size on the fuse itself? It may say 100a on the carrier but it may be an 80a inside?

 

[Guitarist]

If 16mm were already there then fair enough. When installing new though I would fit 25mm on 100A, no question.