Wire Capacities

[Latte]

Hi Guys,

Strange incident today, got called out to an LG and the unit WASN'T at Fault .

Cant remember the unit but the max loading according to the label was 22.5amps.

Now 4.5mm wire from the board to the outdoor iscolator but then 1.5mm to the unit and then onto in AHU.

Found both the 1.5 to the unit and the iscolator burnt out. Now i am fairly sure that 1.5 should not be able to handle this current but there is another unit on site wired the same.

I have replaced the iscolator from a 20 to 32amp and fitted 2.5mm cable to the outdoor from the new iscolator.

Does anybody have a list of what size wire can be used up the what current draw

Regards

Fatboy

[Peter_1]

I have it for Belgium but I suppose you're looking for a UK list.

[walden]

I would have thought that 2.5mm² cable is a little small for 22.5 amps. Without knowing the method of installation it is not possible to give an exact answer but I would be looking at 4mm² or maybe 6mm².

Look at connections! A loose connection will make heat and the heat will run up the copper cable and melt the insulation quite a distance from the source.

[afeef]

http://www.svapowerproducts.com/html...t_colored.html

try this awg standard, you will find your requirment
regards

[malik55]

Hello Fatboy,
You have to check your power supply authority standards as there are variations due to ambient temperature,
Here we are using British standard (BS6004&BS6346) and according to that <1.5mm=10amps/2.5mm=15amps/4mm=20amps/6mm=25amps/10mm=40amps/16mm=50amps/25mm=60amps>also note that capacities are different for single phase and three phase conductors, for the installation and with safe factor it will be better to use 6mm conductor,
Regards.

[colinmcmanus]

How about looking it up in the 16th Edition IEE regs. It will tell you how to calculate for cable size for any situation.
If you can't work it out call a proper Sparky!!!!!!!

[NoNickName]

It also depends whether wires are deployed naked, in tubing, in trunk or buried.l

[frank]

As a rule of thumb

1.5mm = 19A
2.5mm = 27A
4.0mm = 34A

Taken from the 16th Edition. But you must always double check using the formula for volt drop = (Mv/A/m x Lb x L)/1000

or in laymans terms

Millivolts/per Amp/metre x running current x length divided by 1000

if the answer is below 9.2V for single phase or 16V for 3 phase then the cable size is OK.

The Millivolt per Amp per Metre is taken from the relevant cable size table (6D2). Once you have the result you must then apply the correction factors for Thermal Insulation, Ambient Temperature, Grouping and Installation Method.

[rbartlett]

Franks making it sound easy but he is 16th ed (like moi)

we had a few scares re power supplies so we now have set up our own guidelines for mains. We also have set up our own electrical company which means we can shift the responsibility ;-))

however I would not personally use anything less than 2.5 for mains whatever the rating says in any case

up to 20a c/b -2.5mm
up to 32a c/b -4mm
up to 40a c/b 6mm

however there are many factors which should make those spec'ing/installing cables, fuses and circuit breakers put a little time and effort into their selection as it must be noted that you are criminally responsible for any of your poor electrical installations if you don't...

cheers

richard

[chillin out]

If you can't work it out call a proper Sparky!!!!!!!

My mate got called to a cellar cooler because it was tripping, when he arrived he found that a "proper Sparky" had disconnected every wire in sight!!!!

My mate found the problem within a few minutes and then told the customer to tell that "proper Sparky" to get his a$$ back to reconnect all the wires as surely he would have written them down,(wouldn't he?)

(2 indoor, 1 outdoor remote control box)

Chillin

[Peter_1]

In Belgium it is when used normal twisted cable
16A= 1.5 mm²
20A= 2.5
25A= 4
32A= 6
40 A=10
63A = 16

If it's burried, then AMPS can be increased.

Colin, you doesn't need a Sparky to write down this table.
And remember this, a good refr tech is mostly a very good sparky ( and a good solderer or welder) but a very good sparky is never an average refr tech.

[phil]

come on you lot

you have given him all the correct cables sizes

WHAT SIZE IS THE CIRCUIT BREAKER AND WHAT TYPE ??

1,2,3 ABC

sounds like hes got the right idea about the cable wot about start up currents and loadings on the whole installation???

[phil]

come on you lot

you have given him all the correct cables sizes

WHAT SIZE IS THE CIRCUIT BREAKER AND WHAT TYPE ??

1,2,3 ABC

sounds like hes got the right idea about the cable wot about start up currents and loadings on the whole installation???

Part p is not just for christmas it is for life

[frank]

Well, the breaker must be sized just above the running current (load) and the cable must be sized above the breaker.

So, if you had a motor with a FLC of , say, 15A you would select a 20A breaker (unless the manufacturer staed otherwise). The cable size must then be selected using the formula that I gave previously.

Start currents do not apply to cable sizing. Method of starting is applicable to start currents.

[Abe]

Frank

what is FLC ??

thx

[Robert Rumpff]

I got that one Frank ...FLC is Full Load Current (Amps)..

Frank if that's your caddy in your Avitar I want to take up Golf and I want to golf at your course everyday.

[Slim R410a]

Does this not also depend upon type of cable is installed?

Iv'e got some lsoh 2.5mm, which is like a pre-wired conduit and its manufacturer rates it to 35A. Think sparks call it ftx cable or simliar. Its expensive but saves time on smaller jobs rather than putting swa in. I have had sparks many times use this cable on a/c gear I have installed, from where I found out about it.

[Abe]

Slim

Would u have a pic on this cable ?

thx

[frank]

Does this not also depend upon type of cable is installed?

Yes it does. There are different tables for different types of cable from singles to SWA and all between.

Why not buy a copy of the 16th Edition. For around £35 it's a good investment and a boring read

[Slim R410a]

Yes it does. There are different tables for different types of cable from singles to SWA and all between.

Why not buy a copy of the 16th Edition. For around £35 it's a good investment and a boring read

Il bear it in mind.

[Electrocoolman]

Hi,
I'm reading the replies posted with interest.
As a qualified electrical engineer (MIEE now MIET) there are several things to consider when considering the cable size required.

1) What is the max running current and what is the manufacturer's recommended circuit capacity. (ie the latter would allow for high starting currents).

2)The max cicuit capacity and starting current will determine the type of circuit protection device (fuse / mcb). With mcb there are trip ratings...2 or B are the standard....3 or C are capable of higher surge (motors)..and 4 or D are even higher surge. With fuses we have the type of fuse to consider eg 'motor rated fuses'

3) The protection device is to 'protect the cable' (and sub-circuits) connected to it, thus the cable must be able to carry the rated current of the device plus the fault current for the time before the device trips or blows.
An example is a lighting circuit using 1.5mm wire...a fuse is normally 5A, but when using a mcb the rating can be increased to 10A (type 2 or B) due to the time and sensitivity of the protection device.

4) The cable rating is then affected by 'derating factors' which depend on method of fastening and routing, heating effects of adjacent cables and Insulation etc.
This is where the 16th ed 'cable tables' come into being...most are published in guide books to the 16th ed regs....there is no need to buy the complete regs in which you would get bogged down by anyway.

5) Type of cable and construction then come into play...eg 1.5mm SWA can carry a higher current than 1.5mm Twin+E.

6) If you are running in a new circuit, you have to consider the length and the voltage drop and check that it is within limits....again from the tables.
(This is comparable to the pipe size and pressure drop in our business).

7) We now have our cable specification and size. We must not forget that any equipment such as Isolators or connectors need to be specified for at least the circuit current capacity.

8) Finally we need to be aware of sub-circuits and their protection.
A good example of this is the UK 13A plug.....it is often plugged into a ring circuit protected @ 32A.
The cable connected to the plug might be 0.75mm supplying a table light....this cable is rated for 6A. The fuse in the plug needs to be either 3A or possibly 5A....clearly a 13A fuse would present a risk to the cable.
Putting this into our realms, we need to consider the cable between the indoor and outdoor units on a split system....what power does it need to carry.?...full unit power or only power for the indoor unit.

....consider the following example and the Safety Implications:

I recently had to fit a large single phase multi-split system. As it was an inverter, it had a low start current of 1A and a running current of about 10A. The manufacturers recommendation was to connect to a circuit with a capacity of 30A. Thus the mcb was 32A, the circuit cable was 6mm, the isolator was rated for 40A, the cable between the isolator and condensing unit was 6mm (though probably 4mm would have done with the length, and location). When the circuit diagram was studied (confirmed by examining the condensing unit wiring) it was noted that the connections to the indoor units were just tapped off of the power input connector....there was no fuse of any description present.
The indoor units have a current demand of less than 1A....fan and electronics....thus they did not require wiring in anything more than 1mm multicore. In order to use this size cable I fitted inline fuses to each supply feed from the outdoor unit, thus protecting the cable and indoor unit and any drain pump. The fuses fitted were 3A which gave plenty of scope for the drainage pumps as well.
If this had not been done (ie fuses fitted) there would have been a fire risk or alternatively the cable size to the indoor unit would have needed to be 6mm!!! Obviously totally impractable, very expensive and fuses would have been needed for the pumps anyway.

The safety of the units (CE marked) were questioned with the manufacturer as to the lack of fuses. Needless they had an unsatisfactory answer!

I plan to bring the point up at the next RAC show with other manufacturers, but please bear in mind the points raised and safety implications on all your installations.....that is being competent.

Adrian.