Outdoor Flex Cable RR-F or RN-F

[TaylorD]

Hi All,

I have an Halogen Floodlight wired to a 20A JB situated on an external wall with no IP4X protection. I intend on ripping it out and rewiring it and replacing the floodlight with an LED alternative.

However the issue I am having right now is regarding the cable.

I planned on using H07RN-F or H05RN-F cable. This is because both of them are rated for outdoor use, can deal with UV exposure and both can handle the typical temperature range.

However with both of these flex types they only seem to be commonly available in 0.75mm or 1.5mm

1.5mm will not fit through the cable gland into the light fitting. normal VV-F wont fit, so i doubt RN-F will.

0.75mm is only rated at 6A, the light needs to be fed from the Lighting Circuit, which is protected by a 6A MCB (Split load CU so there is RCD protection). As the MCB will never trip exactly at 6A, I believe the 0.75mm cable is not acceptable as there is the potential (though unlikely) that the cable could overheat and burn out before the MCB trips.

So really i need to find some H05/H07RN-F 3G1 cable (3 Core, 1.0mm CSA)

But i cant seem to find it anywhere!

Local wholesalers have claimed they do, ive turned up to buy it and it has been H05/H07 "RR-F" and not "RN-F" one supplier tried to palm me off with VV-F saying it was rated for outdoor use.

Looking at Datasheets from LAPP etc, the RN-F seems to be the only type with a manufactures rating for outdoor use. RR-F does not have a manufactures rating for Outdoor use, but it is still a rubber coated flex cable, Would RR-F be acceptable?


thanks,
Taylor

 

[westward10]

I believe you are over thinking this, you say though unlikely in your post. Yes it is unlikely, 0.75 should be perfectly adequate. Do you have the newvfitting has many come with a fitted flex.

 

[multimick]

it's a fixed load so really only needs proection for short cicuit not overload protection

 

[Marvo]

.................0.75mm is only rated at 6A, the light needs to be fed from the Lighting Circuit, which is protected by a 6A MCB (Split load CU so there is RCD protection). As the MCB will never trip exactly at 6A, I believe the 0.75mm cable is not acceptable as there is the potential (though unlikely) that the cable could overheat and burn out before the MCB trips........

I'm really confused by this. Why do you think is not appropriate to protect a 6 Amp cable with a 6 Amp MCB?

Yes, the MCB won't trip immediately with a marginal overload but likewise the cable won't spontaneously combust or catastrophically fail with a marginal overload either.

 

[TaylorD]

Sorry I realised I missed off part of the circuit.

There are two light fittings

1x 22W LED Floodlight, comes with a factory fitted Flex, H05RN-F 3G1

1x Wall mount light, this does not have a flex, but has the cable gland which does not allow the larger size cables.

As the LED floodlight already has 1.0mm flex, it was another reason why i was not going to use the 0.75mm.

While i know it will be fine running on 0.75mm, the fact is it is only rated for 6A before any kind of derating and I have a 6A MCB.

 

[Marvo]

If it's in free air there should be no reason to derate.

 

[westward10]

I thought 0.75 was rated generally at 7A but that is not really relevant, the chances of a short length of cable to a light fitting overloading to the point where is catches fire are all but zero.

 

[littlespark]

It basically the same as the piddly bit of flex in a normal light pendant. Dropping from 1.0mm or 1.5mm down to the lampholder in something much smaller, which in the good old days could have had a 100W lamp in it.

 

[Gavin John Hyde]

Ho7 is stocked in pretty much every size and sold by the meter in CEF branches. also very reasonably priced too. failing that if you really what some in a larger csa order it from an online electrical supplier.

 

[westward10]

I think if the gland at the fitting does not accept a larger csa that says it all.

 

[TaylorD]

If it's in free air there should be no reason to derate.

True,

It is just i have always been of the belief that the fuse rating must be less than that of the cable, not equal to.

Afterall the fuse/MCB is there to protect the cable, not the appliance.

But that said, most appliances either fail to earth and would cause an RCD trip, or fail short circuit, in which case the likelihood of it drawing exactly 6A for a prolonged time is non-existant, it would most likely trip "instantly" >5x the rating.

But my regs book is there, and it doesnt feel right...

So far the amount of time ive spent on this, probably far outweighs the cost of a different light fitting which can take 1.5mm...

 

['mr2'gd4u]

I thought 0.75 was rated generally at 7A but that is not really relevant, the chances of a short length of cable to a light fitting overloading to the point where is catches fire are all but zero.

7a-8a depending on where you read/which manufacture you use

 

[TaylorD]

As I do have 5M of H05RR-F 3G1 sat in the office, does anyone know if this cable is infact suitable for outdoor use? Or is it only the RN-F type which is?

 

[Marvo]

True,

It is just i have always been of the belief that the fuse rating must be less than that of the cable, not equal to.

Afterall the fuse/MCB is there to protect the cable, not the appliance................

No, if your cable has a rated current of 6A according to it's length, installation method etc then you can install a 6A MCB to protect it. The rated current given to the cable already has safety margins built into it so no further derating is necessary.

 

[westward10]

The best flexible cable for outdoor use is H07RN-F but providing the cable is black and not prone to mechanical damage it will be fine.