Cable Size Question

[jcalow]

Just bought some new powered PA speakers and need to extend the mains cable to each a little. I am a bit confused on the cable size to use though. The plug supplied with each speaker has a plug fitted with a 13A fuse and the attached cable is 3 core 0.75mm2. I went to Maplin and bought a length of 3 core 0.75mm cable. However the ticket they have on the cable reel called the cable "6A 3 core 0.75mm2 mains cable". Is this cable suitable? it looks I dentical to the cable provided with the speakers but why would they fit a 13A fuse if the cable only takes 6A? I don't believe the speakers run at anywhere near 13A.

Many thanks,


Josh

 

[ColJack]

is it the mains cable or the speaker cable you are trying to extend?

if it's the mains, then buy an extension lead or move it closer to the socket.. simples..

since you say that it looks identical to the speaker wire then the cable you've purchased in unsuitable for mains most likely..

 

[crunchynut]

Plug top fuses are commonly available in 3,5 & 13A.

You can also (easily) get 1,2,7 & 10A though. Not sure about 4/6/8/9/11/etc tho!

What power, in watts, does your PA potentially draw? Look on back/side/or the manual of the unit. If you can find the wattage then take your power (eg) 2300W and divide it by your voltage 230V which would equal 10A.

If you have a 2000W cab this would be 2000W divided by 230V = 8.7A.

If you definately know that the existing flex is .75mm then I would change the entire length to a suitably longer one in .75mm flex. This would involve opening up the PA cab but if you just cut it (the flex) and joined it then it would have a weak point. This I would consider OK if it was not on a portable unit that is likely to get knocked about a bit.

Hope that makes sense!

If still unsure then do as CJ says and simply use extension leads.

 

[Adam_151]

The load of the system is most likely sub 6A but with a high inrush current given what you have told us. I do not do PAT testing on a daily basis so I cannot remember the details but AFAIK (and it tallys with sound engineering priciples etc*) but in such a situation fusing at 13A is acceptable subject to a macimum flex length, but I cannot tell you what the permitted length is off the top of my head. I recommend that you use an extenstion cord rather than mess around trying to extend flex



*pun not intended...

 

[OwainDIYer]

The maximum flex length is the issue, a 13A (or 16A circuit protection in Europe) fuse will clear a fault quickly enough on a short thin flex - which is why appliances are sold with stupidly short flexes - but not necessarily on a long one.

I seem to remember for extension leads, 0.75mm okay for 7.5 metres, 2.5mm okay for 25 metres (but might not fit an ordinary 13A plug)

Isn't the mains lead for the PA detachable?

 

[ericmark]

0.75mm is now the smallest flex permitted Table 52.3 and should be protected with a fuse or MCB rated 6A. Historically 0.5mm was 3A and 1mm is 10A with 1.25mm allowing the full 13A. One the continental system 1.5mm will allow the full 16A. It is considered the fuse is to protect the cable and the two common sizes of cable are 0.75mm and 1.25mm so in real terms the 5A and 13A fuse is all that is required however 3A and 13A are the preferred sizes.

433.2.2 allows the protective device to be within 3 meters if is installed in such a manner as to reduce the risk of fault to a minimum.

Can't really see how this can apply to a flex?

Table 41.2 gives the max ELI for a 3A fuse as 16.4 ohms so it will still allow 14A to flow for a short time (less than 0.4 seconds) so most start up surges can be handled.

I would think the wrong fuse has been fitted and I would change to a 3 or 5 amp.