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Posted By Jane Watts
I know it's not good practice etc etc, but is it mentioned in any of electrical publications anywhere?
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Posted By Frank Hallett
You'll find it mentioned by implication in loads of places Jane.
I presume that you're after a "why we don't do it" response?
If so, it's all to do with boring technical stuff such as:-
using different sizes of cable so that the current drawn may be higher than the rating of one [or more] of the intermediate cables: &
creating an unacceptable drop in voltage at the operative end due to distance x individual wire size; &
every connection introduces the ability for "hot-spots" to be created due to poor connection causing current rise, heat generation & voltage drop.
There are also the issues of unexpected disconnection, un-seen additional units inserted, fuse maintenance & replacement; and of course the traditional trip, damage and similar problems.
Frank Hallett
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Posted By Jane Watts
Hi Frank, it's always easier to show people in the work place in a publication which says why we shouldn't do it, you know what people are like, specially techies, they like to argue the point:)
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Posted By MungoDundas Don't have the IEE guide to portable appliances to hand, but I'm sure they frown upon too many leads. That said, the IEE often use Philedelphia lawyers speaks to state a simple point. http://www.iee.org/Publi.../index.cfm?book=WR%20233In theory, the first fuse should pop if the daisy chain draws too much current. Easier to go along the tripping hazard route or, alternatively, hindering the cleaner in bona fide vacuuming duties.
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Posted By John Webster
Jane
To expand on Frank's response, I will try to give you a technical explanation in laymans terms. When current flows through a cable, there is a resistance to the current flow which causes the cable to warm up. It also means that the voltage available at the end of the cable is reduced. Normally, cables are rated to minimise these effects and sized accordingly. If there is a fault, or the cable is overloaded, the fuse will blow to provide protection.
If the lead is extended without increasing the thickness of the conductor, the resistance increases proportionally. The cable will heat up more and the voltage loss could be sufficient to cause the attached equipment to malfunction. More seriously, in the event of a fault the resistance in the cable may be so high that the fuse fails to blow at all, offering no protection. Under those conditions, not only could earthed equipment become "live", but the cable could catch fire.
So, simplisticly, if you have 2 extension leads rated at 10 amps (2.4kW at 240v), then daisy chained they can only carry 5 amps. 3 leads and they would have to be downrated to 3 amps etc.
The danger of course is that they may still be fitted with 10 amp (or 13 amp!) fuses!!
Hope this helps
John
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Posted By Jane Watts
Hi all, thanks for you detailed responses:)
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