Brand new to the Forums and need advice

[AntHalls]

Hi Everyone
I figured I needed to join a forum to ask for advice and learn from it. I have no formal experience as an electrician, but attempt to understand things when needed. I am actually a Sculptor by trade and an Artist. I am a member of the Herefordshire Guild of Craftsmen and we have to deal with setting up electric extension leads and lights at several shows during the year. This week we had a directive from a venue stipulating changes in safety. In the past, each member taking part in a show would take control of their own space and power up accordingly. This has all changed because of the classic 'Daisy Chaining' of extension cables. We have been given a restriction of 3 cables in a line and no more than 7 metres in total length. When you have got 27 members taking part ( in a weeks time ) and 7 twin supplied sockets, you have to use the dreaded daisy chaining. The restrictions now at least make it a little safer, but never ideal. It is always a temporary hook up of usually 2 to 4 day shows. Someone in the group has had to put their hand up and say 'I will'. That would be me then!!! I am going to use a 'star formation' of a 4 bar cable, to feed another 4, then another 4 cables. Still restricting each a run of 3 cables capped at 7 metres. This is acceptable at the venue. I am having to ask every member for their individual wattage ( everything is PAT tested ) to work out their total amperage. That is easy enough and I understand there is a limit to the wattage/amperage across the 3 cables. Each power socket supplied is 3KW and I have to make sure the 4 members plugging in do not exceed the total amperage across the 3 cables. Where I am struggling, is understanding why there is an amperage drop through each cable. The venue paperwork I have states that 1 cable extension should not exceed 12 amps. Where 2 cables are in the line, the total amperage of appliances connected to them must not exceed 10 amps. Where the third cable is used, the total amperage of the appliances connected to them must not exceed 7 amps. Why does the amperage drop as more extensions are added to each other? What I face is having to restrict the members to just 2 of their own cables. I am going to ensure the first extension cable in the line of 3 is a Guild cable or master cable. I have to also ensure the master cable is of good quality and will have to have a 1 metre lead. Short yes, but I have to allow members to reach their appliances with up to 6 metres. Can a 13 amp Ex Cable have a 10 amp and then another 13 amp plugged in a line? I ask this because they may have a mixture of cables. They may hook 3 up with different amperage maximums. I have been looking online for a decent 1 metre lead extension cable that I can use as the master/ 1st in line. There is a cable in Argos with 4 sockets, each with a switch and surge protected. I need to purchase 14 extension cable for next weekend. Would I be safe buying these? This is the last big show of the year for the group and before next year starts, every member will have to alter and adapt. We use the same venue 3 times a year. I will make sure nothing is overloaded. It is unfair to place these restrictions with such short notice, but it has to be and without qualification, I have had to say I would take charge. I have for some time thought about going on a PAT testing course. I would love to learn more. Any way, thanks for listening, sorry for a long first posting, but I am in need of your advice.
Thanks

Ant

 

[Richard Burns]

Welcome to the forum.
Unfortunately there are many issues regarding temporary power supplies that would be impossible to summarise on a forum.
Many installation electricians would be shaking their heads in disbelief at what you propose and many event electricians would be saying what is the problem with such a simple set up.

Essentially what you are planning is not ideal as you are aware.
Any joint in a cable can cause problems of overheating and risk of fire, this will be why the current rating is dropping as you add joints, to try to reduce the risk of a high current load being drawn through multiple possibly failing connections.

Even though theoretically each supplied socket can take 13A (3kW) if you are planning on loading all of the supplied sockets to this level you will not only trip out the supply you will also be overloading the sockets as they are not designed for more than 20A in total from a double socket assuming you are supplied with standard UK house sockets.
It is likely the total current you could take would be in the region of 16-32A (3-7kW) in total for all your power requirements.

Any extension lead or multiway distribution point should be selected to be rated for 13A as this will minimise problems because the cable will be bigger and connections should be of better quality (though Argos may not be the best quality supplier but should be OK). The switches on switched multiway blocks are often causes of failure.
So long as the load does not exceed the minimum rating of any cable in use then it should be OK. eg. 13A, 6A, 10A leads maximum load 6A.
Overall you appear to be hoping to use far more power than I think would be available from the supply.
It would be best to check with the venue the maximum power in total that you can take and work back from there.

 

[AntHalls]

Hi Richard
Thank you for answering this. It is by far the clearest answer I have been given from anyone. I now understand the drop in amperage through the chain. I am gathering the breakdowns of all the members amperage requirements and will place those together working from 1 supplied socket, making sure they are all well under the limit between them. Several members require only as little as 0.3amps working a few low powered lights. The most amperage required so far from an individual is 4.9 amps. I have listened to your explanation with the switched extension cables and will steer clear of those. I did wonder if I would purchase plug in RCD units for the mains sockets and then plug the cables into those at the start. I assume this would at least add some protection to the system?

Thank you once again and I now have a much clearer understanding.

Ant

 

[Wilko]

Hi Ant and Welcome to the Forum !
Can you clarify what is the source of power?

 

[Des 56]

I would purchase plug in RCD units for the mains sockets and then plug the cables into those at the start. I assume this would at least add some protection to the system?

The Rcd for the mains sockets will protect against earth faults
It will not however,help in any way whatsoever with your basic problem of limited supply,multiple outlets and being cautious with possible overload of extension leads

Ensuring correct fusing of the plug tops for the rating of the various extension leads would be more relevant

 

[AntHalls]

Hi Wilko. The source of power are twin sockets @ 3KW each, running off mains supply. I am having to calculate everyone's consumption to make sure they are not using more than I am allowing them to use. One thing that has dawned on me is calculating the amperage drawn from one member. She has 13 single spot 3 watt LED lights that each run off a transformed power source of 4 volts each. I understand the calculation of amperage, but do I calculate from the 240 volts or the transformed 4 volts? She would plug 6 of them into one extension bar lead. So, is the total amperage of the 6 in the bar running 9.75 amps @ 4v, or 0.16 amps @240 volts ? I can't allow more than 7 amps in total between the 3 daisy chained extension leads. I am working on lets say, all 13, 3 watt lights @ 4 volts calculated with 39 watts divided by 4 volts = 9.75. Already she is over the amperage limit. If it were calculated with the 240 volts I am at 0.16 amps for all 6.

Thanks for your involvement

Ant

 

[AntHalls]

I would purchase plug in RCD units for the mains sockets and then plug the cables into those at the start. I assume this would at least add some protection to the system?

The Rcd for the mains sockets will protect against earth faults
It will not however,help in any way whatsoever with your basic problem of limited supply,multiple outlets and being cautious with possible overload of extension leads

Ensuring correct fusing of the plug tops for the rating of the various extension leads would be more relevant

Hi Des 56.
I appreciate you explaining that to me. Another re-think, unless it would still be wise to use them to protect against an earth fault. Everyone's equipment is PAT tested, but I do understand that after the PAT test, anything can fail for a given reason. I am not qualified with electrics in any way, but am trying to apply common sense with it all.

Thanks

Ant

 

[Taylortwocities]

anything can fail for a given reason.

Anything can fail, and it usually does at the most inconvenient time. Its called the law of sod.

Even if the equipment at the end is all PAT tested and working, there is the cable itself, and the plugs and sockets, they are a common source of problems.

And how about the longer lengths of extension, are these in reels? Are the reels fully unwound, or does some remain on the reel? Have you thought about what happens to a coiled reel of cable when electricity is flowing through it? The cable heats up, and can melt, and catches fire.

That's why this sort of installation is now covered by the Wiring Regulations and should be carried out by a suitably qualified electrician.

Here's the problem

I have no formal experience as an electrician, but attempt to understand things when needed.

You don't know what you don't know. As Donald Rumsfeld said - unknown unknowns.

You'll only learn about it when you mate's trade stand catches fire.

Some reading for you http://www.gsa.ac.uk/media/1243850/GSA-Guide-to-Safe-Use-of-Electrical-Extension-Systems.pdf

 

[AntHalls]

Hi Taylortwocities.
Thanks for your input. We have already been told we can't use wound reels. Also everyone's cables etc are PAT tested. I fully understand you telling me I don't know what I am doing, I am applying common sense and trying to make sure no one uses more power than they should be doing. The group I am in has been connecting up this way for over 20 years, and while nothing has ever gone wrong in that time, I know that something could. The venues new directive is attempting to reduce risk by implementing these sanctions. This time next week we will be setting up the show, so no time to bring in a professional, and by next year we shall seek advice from a qualified electrician and sort this out properly.

Ant