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H07 RNF cable
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JonB67 View Drop Down
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Two pair sub cable.  
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odc04r View Drop Down
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Originally posted by MattStolton MattStolton wrote:

Originally posted by odc04r odc04r wrote:

Domestic regs say it is good for 32A continuous afaik as long as it clipped direct, aka in free air so long as it was all unrolled and had adequate cooling sure it'd be fine. But you are on the limit so I'd probably go 6mm for piece of mind.




Domestic regs, I presume BS7671 (18th ed), has a table for H07?

H05, PVC armoured and T&E, and a few other BS(EN) standard install cables have table space, but can't think of a domestic application for H07?

HO7 is only specified in BS7909 as its insulation is 450/1000V, and bendy enough when cold, as thin litz. Detailed spec, i.e. voltage drop/R per KM for a CSA, is down to individual manufacturer, and their tables?

My copy of regs is in the office, so can't check it, as at home, so please feel free to state a table number to put me right.


Oh no, not H07 per se. I was commenting solely on the current capacity of a 4mm cable.
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odc04r View Drop Down
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Points: 5482 		Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 09 July 2020 at 1:46pm
But y'know, original quesiton was pretty open ended. I agree with other points, 4mm can take 32A reasonably safely in some cases, but they do tend towards the marginal side. By the time you have factored in the possibility ofchaining cables and covering large distances you'd be daft not to go 6mm. I'd use 4mm for short non-chained 1-2m runs e.g between distro and racks without worry.
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Originally posted by odc04r odc04r wrote:

Originally posted by MattStolton MattStolton wrote:

Originally posted by odc04r odc04r wrote:

Domestic regs say it is good for 32A continuous afaik as long as it clipped direct, aka in free air so long as it was all unrolled and had adequate cooling sure it'd be fine. But you are on the limit so I'd probably go 6mm for piece of mind.




Domestic regs, I presume BS7671 (18th ed), has a table for H07?

H05, PVC armoured and T&E, and a few other BS(EN) standard install cables have table space, but can't think of a domestic application for H07?

HO7 is only specified in BS7909 as its insulation is 450/1000V, and bendy enough when cold, as thin litz. Detailed spec, i.e. voltage drop/R per KM for a CSA, is down to individual manufacturer, and their tables?

My copy of regs is in the office, so can't check it, as at home, so please feel free to state a table number to put me right.


Oh no, not H07 per se. I was commenting solely on the current capacity of a 4mm cable.


OK, missed your generalisation, which now makes sense.

4mm tends to conduct only just enough to supply 32A. Looking at Appendix 4, and the tables 4D1A etc for Copper conductors, without applying any derating factors, plenty of examples of under 32A capacities. MICA ("pyro") is the only real exception, the copper sheath obviously radiates heat away well to allow the conductors to glow, although it does mention ambient of 30degC, but Sheath operating temperature of 105degC!!
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MattStolton View Drop Down
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Got my BS7909 out now, and cross referencing it to BS7671.

If it is a 60decC, use BS7671 table 4F1A. If 90degC, use BS7671 4F2A.

If three phase in one outer sheath (i.e. 5 core), 4mm cannot supply 32A without getting too hot.

For single phase, only a 4mm2, IF 90degC rated, up to 18m maximum length, is possible, as rated at exactly 32A. However, if any derating factor is applied, it will drop below 32A capacity, and a smaller supply fuse must be used. 60degC rated is not rated to carry 32A.
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Originally posted by JonB67 JonB67 wrote:

Two pair sub cable.  
With 3 core? 
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odc04r View Drop Down
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Originally posted by MattStolton MattStolton wrote:

Got my BS7909 out now, and cross referencing it to BS7671.

If it is a 60decC, use BS7671 table 4F1A. If 90degC, use BS7671 4F2A.

If three phase in one outer sheath (i.e. 5 core), 4mm cannot supply 32A without getting too hot.

For single phase, only a 4mm2, IF 90degC rated, up to 18m maximum length, is possible, as rated at exactly 32A. However, if any derating factor is applied, it will drop below 32A capacity, and a smaller supply fuse must be used. 60degC rated is not rated to carry 32A.


Would say that sounds very logical and pretty much in line with what I expected. Ok for short runs in open air and that's about it. 90C rating is interesting, again makes sense. You'd have to really punish a cable to make use of that safety factor but then what else are regs for...
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Originally posted by Digbethdave Digbethdave wrote:

Originally posted by JonB67 JonB67 wrote:

Two pair sub cable.  
With 3 core? 

You seem to have found a minor flaw in my suggestion.
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Originally posted by JonB67 JonB67 wrote:

Originally posted by Digbethdave Digbethdave wrote:

Originally posted by JonB67 JonB67 wrote:

Two pair sub cable.  
With 3 core? 

You seem to have found a minor flaw in my suggestion.
It happens. 
Be OK for sub links. 
Well some people run cable from amp to box. 
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Sonic the hedge View Drop Down
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Originally posted by odc04r odc04r wrote:

Originally posted by MattStolton MattStolton wrote:

Got my BS7909 out now, and cross referencing it to BS7671.

If it is a 60decC, use BS7671 table 4F1A. If 90degC, use BS7671 4F2A.

If three phase in one outer sheath (i.e. 5 core), 4mm cannot supply 32A without getting too hot.

For single phase, only a 4mm2, IF 90degC rated, up to 18m maximum length, is possible, as rated at exactly 32A. However, if any derating factor is applied, it will drop below 32A capacity, and a smaller supply fuse must be used. 60degC rated is not rated to carry 32A.


Would say that sounds very logical and pretty much in line with what I expected. Ok for short runs in open air and that's about it. 90C rating is interesting, again makes sense. You'd have to really punish a cable to make use of that safety factor but then what else are regs for...

Cable thermal ratings depend on the insulation, H07 is 90degC rated. Also that's the conductor temp so the outside of the cable won't be so hot obviously. Unlikely to need a derating factor for trailing cable unless you are planning in running a whole bunch together.

The limiting factor with length is not the current capacity it's the volt drop and loop impedance. Both are ultimately dependent on the source, UK mains is pretty solid and well regulated, but building wiring also has to be considered.

Since copper has a negative thermal coefficient (impedance increases with temperature) the actual load on the cable is what matters. I would suggest  therefore for powering audio amplifiers, which is essentially an intermittent load (with transient peaks) 4mm will be fine for 32A (assuming a decent source), actually I have used it as such plenty times. But wouldn't recommend it for more continuous loads eg lighting. 


Edited by Sonic the hedge - 23 July 2020 at 6:37pm
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TMH Music View Drop Down
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Originally posted by mk2_ginger_biscuit69 mk2_ginger_biscuit69 wrote:

great for meaty long 16A cable runs though!! 
I’ve been looking into making some 16a cables of various lengths i.e 5,10,15 & 20m lengths, but can’t find 16a Cee connectors that accept cables bigger than 2.5mm CSA. Anyone able to point me in the right direction?
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GAZ. View Drop Down
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There isn’t any as far as I’m aware. Reason being is 2.5mm is good for 20 amps, which exceeds the rating of the connector anyway. As such there’s no reason to use anything bigger.
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