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October 21

Electrical extension cord usage

I came across these safety rules, and don't understand them:

1) Extension cords should only be used as a temporary electric solution, and they must be unplugged when not in use. What's wrong with using them as a permanent solution, say to provide power for lighting in an enclosed porch ?

2) Outdoor-rated cords should not be used indoors. Why not ?

3) Never plug one extension cord into another. I realize that this will increase resistance, and that you have to be careful to keep the connection between the two dry, but other than that, is there another reason not to do so ?

4) Never use a wet extension cord. Aren't outdoor cords designed for this ? Using one for lawn work often involves dragging it over dew-covered grass.

5) Never force an extension cord into a socket . I regularly need to apply a great deal of force to get the cord plugged all the way in. Could this cause damage to either the plug or socket ? SinisterLefty (talk) 15:11, 21 October 2019 (UTC)[reply]

The problem (or at least one of them) is damage. They're not robust, they're used in a variety of damaging contexts. A fixed cable - even nailed to a wall with cable clips - will be "out of the way". But extension leads are run through open doorways, where the door can be closed upon them. Or they can become dangerous to others by becoming a trip hazard. You can even damage them when they're not in use – the classic door-chop is just as much of a problem whether there's a load plugged in, or even (for becoming a future hazard) if they're not even plugged in, just lying out and exposed to collecting damage.

They don't increase resistance much, as a linear measure. The greater risk is an increased chance of a high resistance, owing to the greater number of connections. A little cable resistance isn't a big problem because this heat will be small and distributed over a long length - there's minimal temperature rise. A faulty connection - either a weak spring contact onto a pin, or a loosened screw terminal, will produce more heat, and as it does it in one place, that's a serious temperature rise, enough to lead to damage and potentially a fire. The more cables you daisy-chain, the greater chance of one of these having a fault.

Plugs don't need to be forced into sockets. Damaged plugs do, and because extension leads get walked on, they're likely to have the bent-pin damage which makes them hard to insert. So if it doesn't go in easily, something is wrong.

I'm unfamiliar with some US practices and warnings, so can only speak for the UK. It's generally safe to handle a wet cable, but not so much a wet plug or socket, as they involve greater exposure of conductors and surface conductivity can easily give the handler a shock. However there's also a very serious risk where a cable has been damaged to bare a conductor. When dry, there's a touch hazard over maybe an inch of cable. But if wetted, that hazard extends over a foot or more of the cable.

I don't know why outdoor cables shouldn't be used indoors. I do it all the time. We have very few such cables distinguished as such: UV isn't such a big hazard in the UK and we shouldn't encourage permanent installation anyway (and if you do, the cable should be protected, not bare). There are connectors more appropriate for outdoor use, but they're just uncommon indoors rather than forbidden. Some outdoor cables might be extra-flexible (for Winter use without stiffening in the cold) or even heavier gauge rubber insulation which is damage resistant but doesn't age as well. Neither are forbidden indoors.

Something we do have in the UK is regular PAT testing (and yes, that's a tautology). There's no fixed schedule for each appliance needing to be re-tested, that's at the discretion of a tester or facilities manager. But extension leads are right at the most-frequent testing end of this. Some equipment hire operators would test them weekly, or per-hire.

We also have a UK problem with "Part P". This was an income tax rule from a few years ago, which restricted the number of tradesmen who could carry out the simpler fixed electrical work. A side-effect of this was to make minor repairs or extensions much more expensive: rather than a general handyman charging £30 to make a repair, it could be an electrician charging £100. As a result, these repairs just stopped being done. Our plant has become less safe as a result and we've also seen a vast increase in the use of extension leads on a semi-permanent basis, rather than having fixed sockets added. We're starting to see this reflected in accident statistics, mostly so far as trip hazards. Andy Dingley (talk) 15:58, 21 October 2019 (UTC)[reply]

Re: "Plugs don't need to be forced into sockets", I often find that new plugs don't quite fit into the house sockets. It appears to be because dimensions on the plug and socket don't quite match. (However, computer cords often have too loose of a fit to the computer.) That never happens there ? SinisterLefty (talk) 19:44, 21 October 2019 (UTC)[reply]

Our plugs have thick solid brass pins. They're thick enough they can be chamfered on the tip to aid insertion. They're also thick enough that the plausible variation in the contact springs is proportionately less, so less noticeable. If one of our plugs won't insert, it's usually the safety shutter on the socket which has failed in some way. If it's hard to insert, it could be a bent pin from being walked on.

We do get contact problems by interworking shaver plugs and Europlugs. But both are a bodge to start with. Andy Dingley (talk) 22:04, 21 October 2019 (UTC)[reply]

I take it bodge = kludge. SinisterLefty (talk) 22:42, 21 October 2019 (UTC)[reply]

Generally, safety rules are written because someone had to pay someone else a lot of money for getting hurt or damaging some property. So, if you ever want to know what a specific safety rule was written, it's because "someone did this once, and got hurt, and someone else had to pay them a lot of money and no one wants to do that anymore". --Jayron 32 16:12, 21 October 2019 (UTC)[reply]

This is one of many US / UK differences. Our rules are thought up by civil servants. Nor are our damages in such injury cases enough of a disincentive to change policy. We barely have asbestos liability adequately recognised. Andy Dingley (talk) 22:08, 21 October 2019 (UTC)[reply]

If this is USA, the "never force" rule is probably to stop you from cramming a modern polarized plug into a non-polarized socket from the 50s. ApLundell (talk) 14:29, 22 October 2019 (UTC)[reply]

It's also probably to stop you from breaking things. --Jayron 32 14:57, 22 October 2019 (UTC)[reply]

The general rule to not force things together has always been problematic to understand. There's the problem with defining exactly how much force is too much, and then there's the problem of what to do if that amount of force doesn't get the job done. For example, many of my house windows require just about every bit of force I can manage to open. Is that too much ? Do I need to have every window replaced at a cost of thousands of dollars to avoid over-forcing them ? Or should I just continue to avoid any such advice and apply as much force as it takes to get the job done ? (I can always replace the windows if and when they crack from applying too much force.) SinisterLefty (talk) 15:30, 22 October 2019 (UTC)[reply]

Tight windows are not likely to cause electrocution and/or a fire. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:40, 22 October 2019 (UTC)[reply]

And neither are tight plugs in electrical outlets. SinisterLefty (talk) 18:56, 22 October 2019 (UTC)[reply]

Forcing tight pins into sockets (UK design at least) is the second most-likely cause of fires with them (favourite is loose screw terminals).

It shouldn't be necessary. If it is, something is wrong. Commonly (within this rare case) that something is a contact spring which has been folded over. Forcing it in then pushes half of the spring downwards. The other half may still contact, but has minimal contact force. An arcing fault then develops.

Back in the 1970s, we didn't buy stuff from China, we made it here. There was one design of four way extension socket block which had huge dominance over the market (MK Duraplug). The design of this had the contact springs for all of the sockets on a single semi-rigid set of bars. When damaged, the plastic backing to the sockets could be broken off. This was enough to leave the spring bars unsupported - they still made contace, but again it was only a loose contact and there was a risk of arcing faults. As these same extensions were so widespread, it was a fault which some users (lab techs, roadies) learned to spot. Fortunately arcing faults in the UK don't burn our houses down as they do in the US (for several reasons). Andy Dingley (talk) 19:41, 22 October 2019 (UTC)[reply]

Well, there was the recent Grenfell Tower fire, killing 72, caused by an electrical fault. SinisterLefty (talk) 01:12, 23 October 2019 (UTC)[reply]

That wasn't an arcing fault, or in supply wiring. It was an appliance fault in a fridge-freezer from Whirlpool, a US company (Hotpoint branded, but Whirlpool have owned that brand for years now). We also have an appliance fire problem running rife with Whirlpool tumble dryers which has taken years to get any action over.[1] Andy Dingley (talk) 12:02, 23 October 2019 (UTC)[reply]

Yes, but what made the fire deadly was a combo of allowing that flammable building cladding and the fire department telling the residents they would be safer if they remained in their units. Those are UK regulations and policies. SinisterLefty (talk) 19:35, 23 October 2019 (UTC)[reply]

Not according to the article, the cladding was a mix of versions that shouldn't have been used together, according to the manufacturer:The manufacturer, Kingspan, "would be very surprised if such a system [...] would ever pass the appropriate British Standard 8414 large-scale test"

Clearly mistakes were made in giving out the certification of the building, which does not necessarily mean the regulations are wrong Rmvandijk (talk) 07:57, 24 October 2019 (UTC)[reply]

According to the articles, Hotpoint and Indesit Company, the fridge-freezer was manufactured well before Whirpool bought out Indesit and so Hotpoint brand name. I assume this means it was also designed by Indesit or similar. So while the time of the accident, Whirpool was responsible for any design or manufacturing problems with the fridge-freezer that caught fire, they weren't the ones responsible for either its design or manufacture when either of these happened. Nil Einne (talk) 14:53, 25 October 2019 (UTC)[reply]