voltage drop

[justajiffy]

I am trying to find out if when wiring a ring main you lookup in the iee regs the voltage drop for 2.5mm cable or as you are doubling up in effect is it classed as 5mm so you look up what drop they,d be on 6mm as there is no 5mm conductor.Also why can,t i find any tables in the regs for 110v cable voltage drop ? where could i find this information justajiffy

 

[ban-all-sheds]

Use the voltage drop figures for 2.5mm, and work out what the maximum length would be for 9.2V drop at your particular Ib and operating temperature.

The maximum length for the ring cable will be 4 x that length, but don't forget to consider disconnection times based on installation method and type of protective device.

As for 110V - VD is proportional to current, not voltage, which is why there are no tables for 110V.

 

[justajiffy]

thanks for the info ban-all-sheds,as for the 110v ive got to wire about 7 110v industrial sockets on a long about 100m from distribution board and back the sockets themselves are rated at 16amp and i was going to wire them in 2.5mm swa cable off a 30a breaker but it was mentioned i may have to use 4mm cable because of the length but if it is[110v] proportional to the current wondered if there was a formula i could use to determine the correct size cable and breaker for that matter-newly qualified

 

[ban-all-sheds]

It's the same formula that you'd use for a 230V circuit..

You need to know your design current, and in the absence of any other data I guess that'd have to be 30A, if that's your breaker size. I can tell you though without looking anything up, or doing any calculations that 100m of 2.5mm will be undersized.

If you want to work out what breaker you need then obviously you need to know the loading on those 7 sockets is likely to be.

I'm very concerned though - where and for whom are you installing a 110V circuit? What's it supplied from? What's it going to be used for?

And on what basis are you doing it? You say "newly qualified" - are you a qualified electrician, or a qualified something else? Surely if you're an electrician, even a newly qualified one, you'd know the basics of circuit design?

 

[kendor]

I understand from what you are saying that you are running these 110v sockets from a distboard fed from a 110v source?
Although not quite sure if it is still valid but it used to be the case that 110v sockets had to have their earths fed from the centre tap of a double wound transformer so that if their was an earth fault on a piece of equipment plugged into the socket then the fault voltage would not be above 55v

 

[plugwash]

yeah site type 110V supplies are CTE

the good side of this is it means that you realistically only need to achive 5 seconds disconnect in medium risk cuircuits (includeing sockets) because shock voltage is almo0st certailnly going to be less than 50V

the bad news is 5 second disconnect still needs fast trip of the mcb

according to tlcs guide you should not put 16A cees on anything more than a 20A breaker and i personally wouldn't put them on a breaker of more than 16A

based on a 16A cuircuit on a B type breaker you need 80A to fast trip the breaker

for disconnect
V=IR
55=80R
R=0.6875


for volt drop
V=IR
4.4=16R
0.275

soory to disappoint you but you are going to need a bloody big cable to achive 0.275 ohms over 100m

the cable is needed bigger than anything TLCs calaculator knows about!

 

[AdamW]

you are going to need a b****y big cable to achive 0.275 ohms over 100m

the cable is needed bigger than anything TLCs calaculator knows about!

Yeh, but I noticed they don't have any superconducting cables on TLC...

What you need is Magnesium Dibromide, cool it to about -233 Celsius then you won't need to worry about resistance or voltage drop!

 

[justajiffy]

yes the 110v Distribution board is fed from a double wound transformer centre tapped earth so the fault voltage is not more than 55v. The equipment used is all 110v portable.I have since learned the 16a ceeform sockets may be wired only on radial circuits. the number of sockets is unlimited but the protective device must not exceed 20a.If any of these sockets are likely to be fully loaded only one can be used at a time.This would halve my cable run to 50 mtrs as it would no longer need to be wired as a ring main and still dont know where to look to size my cable i,m only an apprentice at this game

 

[ban-all-sheds]

... i,m only an apprentice at this game

Then ask the people for whom you're apprenticing - it's their job to teach you stuff like this. Presumably a "newly qualified apprentice" means you have at 2360 Part 1? Why has your employer given you the task of doing this job without providing you with the support you need? Have they posed you a "if you were asked to do this how would you go about it?" type question? Not sure asking on a DIY forum is the right thing for you to be doing...

I don't know without looking it up which tables you need, but somewhere in the regs you'll find details of the current carrying capacity of the type of cable you're going to be using, and the derating factors that may apply given the method of installation.

Not trying to be slopey shouldered, but your best bet is to find that info yourself, as you need to learn your way round the regs....

 

[Big_Spark]

16A Ceeforms sockets for site use should be in individual circuits if the run to each exceeds about 30m, less if the socket will be used to power any rotating machines that will cause significant volt drop on startup.

Any 110V Tx should not be more than 50m from the point of use of the supply for related reasons.

If this is for site tempories, you would be far better off locating the Tx nearer to the point of use, and then supplying it (if a 10kVA 3 phase unit) with 6mm 4 core SWA clipped/tied at high level to mitigate the risk of damage.

 

[ban-all-sheds]

Welcome back.

 

[securespark]

Ban

See "Where's FWL?"