Voltage drop in conduit

[Danny]

Still new so bear with me ...

Why does Installation Method B (Conduit on a wall) not appear on the voltage drop tables ?

Therefore how does one work out voltage drop for Method B .. ?

Thanks chaps ..

 

[Apache]

Are you confusing voltage drop and de-rating?

 

[Andy™]

voltage drop will be the same for all installation methods - its to do with CSA of cable

 

[Danny]

Yes .. I am getting confused .. I'm planning my assessment job and probably overdoing it a little ... This is my plan and I'd appreciate comment ..

New fixed lighting circuit to the outside rear wall .. Low energy fitting, 2way switching inside and out with the run back to the spare way on the CU .. circuit governed by photocell .. T+E 1.5 flat for the entire run in 20mm black pvc conduit ... conduit chosen for appearance and to protect the cable from heat as the rear wall gets a belting from the sun ..

Should I be using single core for this as it's in conduit or am i fine and just over analysing it ..

 

[Andy™]

singles are usually used in conduit, but T&E does fit and can be used. just dont stuff the conduit full with cable - allow plenty space around it

 

[Danny]

Thanks andy, thats great ...

 

[Apache]

Would white conduit reflect the sun better than black?

 

[green-hornet]

when you design any circuit you have to take into account all de-rating values.

Say for example that you design a circuit with an ambient temp of 30 degrees C.

all your calculations will be based on this, however if you suspect the cable to reach higher temps or is grouped with other cables you will have to apply all the de-rating values associated with the design so that you maintain a stable installation without overloading and more importantly provide overcurrent protection and disconnection times.

Voltage drop is totally different.

You do all the calculations first regarding de-rating then when you have found a suitable cable you then carry out a voltage drop to see if the selected cable can carry out the required function.

To do this you need to find

A supply voltage

B watts or amps

C length of cable run

D power factor

E method of installation (clipped direct normally would carry more amperage)

F protective devise (bs 1361 or others (any circuit protective devise) )

You should then have a suitable cable size.

Under the 17th edition you are now allowed 5% on power circuits and 3% on lighting circuits.

 

[Danny]

Thanks chaps, very helpful ..

 

[green-hornet]

Would white conduit reflect the sun better than black?

Yes it would because black would absorb more heat(reflective) than white.

 

[batty]

I don't think a bit of 1.5 will get overloaded for one low energy light fitting.

Batty

 

[green-hornet]

I don't think a bit of 1.5 will get overloaded for one low energy light fitting.Batty

:^O :^O

I would agree but you should never take anything for granted.

:^O :^O:^O

 

[batty]

:^O :^OI would agree but you should never take anything for granted.

:^O :^O:^O

My thoughts too.

 

[Danny]

Fellas this is all good stuff ... GH that's the clearest i've heard it explained .. many thanks ..

 

[green-hornet]

Fellas this is all good stuff ... GH that's the clearest i've heard it explained .. many thanks ..

No problem every regular on this forum would answer you the same.

Thats why I love, if I can, give the right answer.

We never dress anything up to be complicated, we all know what its like to learn, we are still learning, you young uns teach me a thing or two, and thats for sure.

 

[a1]

Fellas this is all good stuff ... GH that's the clearest i've heard it explained .. many thanks ..

Indeed, There are some great explainations in clear English, given on this forum.

While I think the OSG is Good. I think the "Good Electrician's guide" by the Amicus Union, is better.

Everything that you need to work out the cable / Earth size is all there (all in handy buches).

PS. Welcome to the forum.

 

[green-hornet]

Indeed, There are some great explainations in clear English, given on this forum.While I think the OSG is Good. I think the "Good Electrician's guide" by the Amicus Union, is better.

Everything that you need to work out the cable / Earth size is all there (all in handy buches).

PS. Welcome to the forum.

I would agree with that however my last amicus book was published in 2004.

The Amicus guide to BS7671:2001 Incorporating Amendments 1&2, 2004 16th edition

I really do need to update :^O