Flexible v twin and earth?

[Raspy9999]

Hello. I'm new to the forum and going through training.

I have been getting conflicting advice from a couple of qualified electricians and my tutor and would appreciate some advice.

For the installation of a photovoltaic system with a 1200w inverter about 15m from a new consumer unit, I have been advised to run the a/c in 3core Flexi. This would be clipped through the loft, down an internal wall in conduit and then along a garage wall at ceiling level and finally down the garage wall again in conduit. The reason for the advice was the slightly lower voltage drop.

My tutor thinks it should be in twin and earth but I can't find anything in 7671 that says Flexi can't be used so long as it otherwise follows code.

Having said that, even if it is technically OK but is considered unprofessional, I would prefer not to push it on an install that will be used for an *** assessment.

Any comments welcome.

 

[superspark]

hi m8 and wellcome

i use twin and earth 2.5mm for most pv jobs

i can only tell you how i do it, each to their own as they say.

i run 4mm singles from db in yt 4 trunking into rotary isolator 20a then from isolator to solar meter i sit both isolator and meter on top of yt4 trunking next to db so its all nice and neat.

then run 2.5mm t+e from meter up to loft where inverter is situated with chosen instalation method either conduit or trunking etc, into another rotary 20a isolator then 2.5mm flex from iso to plug for invertor.

it works for me.

we all have our own way of doing things and i,m sure some guys on here have better ways than me.

which we can all learn from and is the reason of the forum to all share ideas.

 

[Andy™]

nothing wrong with flex. you could wire your house in the stuff if you wanted

 

[PC Electrics]

Hello. I'm new to the forum and going through training.I have been getting conflicting advice from a couple of qualified electricians and my tutor and would appreciate some advice.

For the installation of a photovoltaic system with a 1200w inverter about 15m from a new consumer unit, I have been advised to run the a/c in 3core Flexi. This would be clipped through the loft, down an internal wall in conduit and then along a garage wall at ceiling level and finally down the garage wall again in conduit. The reason for the advice was the slightly lower voltage drop. [1]

My tutor thinks [2] it should be in twin and earth but I can't find anything in 7671 that says Flexi can't be used so long as it otherwise follows code.

Having said that, even if it is technically OK but is considered unprofessional, I would prefer not to push it on an install that will be used for an *** assessment.

Any comments welcome.

1. the volt drop will surely be the same!

2. "thinks" huh? Doesn't know

Absolutely nothing wrong with using flex, as long as the type of flex and it's size are chosen to suit the environment and current rating.

I'd choose either TRF (tough rubber flex) or H07RN-F for this application. I'd probably use H07 because it's rated at 80C max (std flex is 60C) and being black can stand to be surface mounted ouside. Also it's conveniently available by the metre from various wholesalers (I use Edmundsons). I'd use 1.5mm in this application since it will be in continuous use and in conduit (personally I think a small black flex looks neater than conduit, 'blends' into walls better).

 

[Sidewinder]

The skin effect does not exist with DC, thus there is no advantage in using stranded over solid from a resistance standpoint.

 

[Chr!s]

The skin effect does not exist with DC, thus there is no advantage in using stranded over solid from a resistance standpoint

I don't think there's much of an advantage in an ac 50 Hz circuit, Low frequency and relativity small cable diameters

 

[Sidewinder]

Plumber,

IMHO that is what I was saying!

At 50Hz the skin affect is so negligible that it is virtually non existant.

The cable diameter will obviously have an affect on the situation as it will directly control the circumference of the wire.

However, IIRC correctly from my undergraduate electromagnetism theory, the frequency is the overriding factor.

It has been a few years mind & I'm not near my reference books for the reset of the week.

 

[Chr!s]

Plumber,IMHO that is what I was saying!

At 50Hz the skin affect is so negligible that it is virtually non existant.

The cable diameter will obviously have an affect on the situation as it will directly control the circumference of the wire.

However, IIRC correctly from my undergraduate electromagnetism theory, the frequency is the overriding factor.

It has been a few years mind & I'm not near my reference books for the reset of the week

You are quite correct, i misread your post, sorry

 

[steptoe]

you will probably find it is a helluva easier to terminate flex to your inverter than T&E,

though I generally run T&E or singles to my local isolator at the inverter then 2.5 flex from isolator to inverter.

whatever floats your boat IMO.