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Sadly they don't explain WHY not to use it with an extension cord. I wonder if it's to do with the risk of having such connections outside in the elements?

The cord it comes with is 7m long, and where we want to site it is 6m from our outhouse. I've drilled a 1ft long hole through the stone wall of the outhouse to thread the spa's cord through... But once in the OH the plug still ends up 3m away from the socket. Would it be considered ok to run a standard 13A indoors extension cord to bridge the gap?

The OH socket is grounded (I'm in the UK) and on an RCD-protected circuit, and the spa has an RCD in its cord (and another in the pump/heating unit, I think).

Maybe their concern is voltage drop in the thinner conductors of a typical extension cord. Maybe I can buy a "heavy duty" one which would be largely equivalent to wiring a new socket in?

Or do I need to just admit defeat and wire a new socket in?

Thanks

Codemonkey
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    What risk are you referring to? – Harper - Reinstate Monica Apr 07 '20 at 12:34
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    The average homeowner doesn't have waterproof extension leads. They have indoor extension leads. So I wondered if the manufacturer's concerns centre around the use of indoor leads outside, and them becoming wet – Codemonkey Apr 07 '20 at 12:45
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    Then they would have said outdoor extension cords only, though. – Harper - Reinstate Monica Apr 07 '20 at 14:55
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    My guess is it is because of the lawyers. If you try to make a list of conditions that you could use an extension cord and somebody gets hurt some lawyer is going to find some weakness and drive explosives through it. That's not to say I think it would be safe or unsafe, I don't know the detailed criteria that they would include if it wasn't for the lawyers.. – NoSparksPlease Apr 07 '20 at 15:12
  • Here is another option, add an outdoor outlet that branches off the outhouse's outlet with an in-use cover. – ratchet freak Apr 08 '20 at 14:37
  • @NoSparksPlease My wife works for a company currently distributing N95 masks and other health care products. She has told me many people are asking "Can I use XXX material as filtration?" And like you say, it's "CYA". They can't give an answer like "Maybe it's better than nothing" because if it doesn't work they'll get in trouble *and also people will get sick.* So if there's any kind of issue with extension cords the company can't say "Maybe don't use extension cords", they can really only safely say "Don't use extension cords." It's unfortunate. – Captain Man Apr 08 '20 at 14:41
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    Well, if it's because of the lawyers, that'd make it alright then. Come to think of it half of NEC is "because of the lawyers" so we can throw that in the bonfire too. – Harper - Reinstate Monica Apr 08 '20 at 16:23
  • The circuit breaker might not activate in case of a short circuit due to the increased resistance in the connection once a (unspecified!) extension cord is connected. That is indeed the real reason. – Peter Kämpf Apr 08 '20 at 18:09
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    @Harper-ReinstateMonica There are very few outdoor rated extension cords available, and anyone who doesn't know about them clearly _doesn't know about them_ so safer for the manufacturer just to say "no extensions" than to say "only use a suitable extension" and get sued for not explaining it properly. – MikeB Apr 09 '20 at 10:40
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    @PeterKämpf I don't understand what you are getting at - if the main cord is adequately specced for 13amp usage, and the extension cord is too, then the circuit breaker will surely work just fine? That's why every part of the system is over-engineered (on paper) so that they are still safe when 'abused'. – MikeB Apr 09 '20 at 10:42
  • @MikeBrockington except what you're doing there is rationalization. You pre-decided that the extension cord is gonna be OK, now, after the fact, you're inventing the reasons why. This is not how you make good logic! "Stupid people" is a favorite whipping horse for such rationalizations, because it **also** makes oneself feel superior. – Harper - Reinstate Monica Apr 09 '20 at 14:59
  • @MikeBrockington: Lawyers have a distinctly different opinion to yours. You and me, we use common sense. They don't, but they write the rules. – Peter Kämpf Apr 09 '20 at 17:08
  • Just don't put a 25m cord between it and you'll be fine. – Mast Apr 09 '20 at 19:49

10 Answers10

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I think you have likely answered your own question. The use of an extension cord could cause a voltage drop, especially since the factory cord is long already and the spa probably has an electric motor that would be damaged by voltage drop. Also, cord/plug connections are not weatherproof.

This is a CYA (cover-your-arse) by the manufacturer. Your plan of using a short heavy duty cord (same wire gauge as the factory cord) with the connections indoor should be fine.

Jimmy Fix-it
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    Note- your plan will work; however, it may void the warranty if there were a problem of some sort and the maker became aware of your setup... – Jimmy Fix-it Apr 07 '20 at 14:09
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    Yes - Short and 10 or 12 gauge - and rated for outdoor. The danger is the extension cord over-heating. Each plug and receptacle adds a small amount of resistance. "Heavy" is also applied to 14 & 16 gauge extension cords. – Programmer66 Apr 07 '20 at 14:46
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    To be clear - I am not suggesting to use 14 or 16 gauge, just that 14 & 16 gauge extensions are also called "Heavy". - Use 10 or 12 gauge. – Programmer66 Apr 07 '20 at 15:02
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    In catastrophic scenarios, improper use of extension cords can even nullify home insurance. Glad you did extra research before messing with electricity. – Nelson Apr 08 '20 at 02:32
  • @Programmer66 the OP is in the UK, where the gauge isn't marked on extension leads. They're marked by a maximum current rating. Heavy duty is 13A because that's the standard for our sockets. 16A extension leads have different connectors and are available in long lengths, to connect caravans; these also have outdoor connectors – Chris H Apr 08 '20 at 10:01
  • @Nelson that's less likely to be true in the UK than the US, though it may not be completely impossible. – Chris H Apr 08 '20 at 10:04
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    Because the cables proper (proper rating/gauge provided) are equivalent the point of problem must be the connector. With household connectors it's probably impossible to guarantee large enough contact surfaces, creating resistors with corresponding heat which with long-running, high-current consumers can be a hazard. Even if it does not start a fire it compromises insulation and plastic case, resulting in potential short-circuits or unintended current paths through carbon. – Peter - Reinstate Monica Apr 08 '20 at 12:01
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    @Peter-ReinstateMonica, even with "equivalent" rating/gauge cables you have a limitation on *length* due to voltage drop. especially as it concerns electric motors. So I don't think the connectors are the *only* potential problem in these scenarios. – Jimmy Fix-it Apr 08 '20 at 14:52
  • You have to think a guy that has an inflatable hot tub is OK with taking a few risks. – DMoore Apr 08 '20 at 16:47
  • The other risk is that the tub's plug has an in-built RCD - using an extension opens the possibility of the extension falling into the tub and nullifying that in-built RCD protection. Given that the feed circuit itself is also RCD protected it's less of an issue for OP, but remain a CYA liability from the manufacturer's point of view. – J... Apr 09 '20 at 16:21
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The basic reason is that if they said, "Feel free to use an extension cord", someone would connect up a 50m, 3A, two-core cable with no Earth and a loose socket. They would then sue the company when it didn't work (too much voltage drop across long thin extension cables) or it caught fire (current drawn exceeds capability of thin extension cables) or they got electrocuted (no Earth).

In reality, if you use a short (2-3m), heavy-duty, 3-core (with Earth), outdoor extension with a good stiff socket and shield it from spillage, you should be OK. However, remember that, as Abraham Lincoln once said, "don't believe everything you read on the Internet".

Oscar Bravo
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    This. "Extension cord" in any "don't use an extension cord" warning means the flimsy things sold at dollar stores, Kmart, Roses, etc. that are rated for 7 amps or less. It doesn't mean an actual proper extension cord with ground and sufficient wire gauge and insulation to safely use with power tools, equipment, etc. – R.. GitHub STOP HELPING ICE Apr 09 '20 at 02:20
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    Considering Lincoln died in 1865, he was truly ahead of his time with quotes like that. – Mast Apr 09 '20 at 19:50
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I have always heard that the reason for the "no extension chords" is because they are not supposed to be used for permanent installations, only temporary, i.e., Christmas lights. Extension chords are pretty cheaply made and the ones I have had fail on me always fail at either the male or female end. If you're going to keep your tub inflated year-round, think about adding a new socket. Enjoy it,

JACK
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8

The manufacturer will be guarding against both voltage drop on the supply (which could affect the operation) and creating too high a fault loop impedance (which could affect the disconnect time of the circuit breaker in case of a fault).

At a guess, a minimum length, heavy duty extension lead will likely be fine.

However, for peace of mind, if you can readily add an extra socket in the right place, I’d suggest that is the correct thing to do.

John
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  • I tried to buy the requisite stuff for a new socket while I was food shopping this evening... I failed; they had sockets but no cable. Instead I bought a heavier-looking duty single socket extension cord, and when I got home I shortened it to the correct length to minimise voltage drop. – Codemonkey Apr 07 '20 at 22:22
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    Just been out to feel it after it's been running a few hours and the cable didn't feel even vaguely warm to the touch so let's hope all is ok! – Codemonkey Apr 07 '20 at 22:23
  • Hello @Codemonkey, I always read, that you shorten the premanufactured cords. I dont think that this is a good idea. Since it is easily done, it still is a flexible and moving cord, that may break when moved around a lot. I could be safer if you installed a wall socket. there are no moving wires in it and the cords plugged into it are still new... – Wolfgang Roth Apr 08 '20 at 10:06
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    This is now stapled to the wall and not moving. It'll certainly do until I get some cable to add a dedicated socket. – Codemonkey Apr 08 '20 at 13:14
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    Four answers down, only here is the correct one: The circuit breaker might not activate in case of a short circuit due to the increased resistance in the connection once a (unspecified!) extension cord is connected. **That** is indeed the real reason. – Peter Kämpf Apr 08 '20 at 18:07
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The issue is electrical drownings

One thing people really don't understand about electricity and water: a shock that would be trivial anywhere else is fatal when water is around.

You're hit with a triple whammy. First, ordinary water and wet skin conduct electricity well, meaning a shock you barely felt before, now has much worse effect.

"Water doesn't conduct electricity" only true for artificially demineralized water; water does not like to be demineralized. Demin is corrosive and will attack anything it can leach minerals out of. The city's water source is not demin, and they don't entirely demin it; it would eat the pipes if they did.

Second, when water is around, a stun is as good as a kill. People in electrical drownings weren't electrocuted to death. They just lost control of their muscles and fell down into the water. They did not raise their nose out of the water because they were unable; either their muscles would not do what their brain commanded, or they were laid unconscious by the fall (or the shock). See how this becomes a domino effect: your legs malfunction, your head cracks the ground, which knocks you unconscious, and then, you drown.

And third, the same thing happens to the people who try to rescue you. In one famous drowning in a fountain, one girl fell, another girl went in to rescue her, the other two went in to help them, and all four died.

That's how it goes; the third or fourth cohort of rescuers recognizes they're looking at a victim and a rescuer who has become a victim, and does not repeat the mistake.

Of course it's made worse by the first factor; people who have been bit in the past and live to tell the tale, start thinking they're immune to electricity, and don't realize they've just been lucky so far due to being in the dry.

There is no way to insulate an extension cord connection. If it gets wet, it will leak current.

"Oh, but my house is protected by the bog-standard Euro 30ma RCD! I'm fine!"

Nope. Personnel protection is not the purpose of Euro style 30ma RCDs. 30ma will stun pretty much everybody, and will directly kill a more vulnerable person. That is why North America requires 6ma GFCIs where the objective is personnel protection (e.g. kitchens/bathrooms/pool areas).

Now, your hot tub's electrical cord may have a lumpy 6ma GFCI/RCD on its electrical plug. Obviously, the extension cord connection will be before that, so, not protected.

Harper - Reinstate Monica
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I have seen the same rules on devices for a bathroom. In my opinion its all about exposing bare wires. If the two (the extension and the power cord) are not a waterproof connection and resting on a floor (very common), then there is risk of shock. That is far more likely in a bathroom (or near a hottub) where water is common.

I believe a better way is to replace the current power cable with a longer, properly rated, power cable. That cable would connect to the hot tub (You will likely have to open up a cover where the current power cable is screwed into the electrical of the hottub) and plug directly into the outlet without any breaks.

Obvious disclaimer: Its better to pay an electrician than trust a random guy on stackexchange.

Robert Lugg
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    This really is the best advice here, not sure why it has not received more votes. – James Jenkins Apr 10 '20 at 17:29
  • If I could easily have bought some external fat-gauge armoured cable in this time of lockdown, I might have gone that route. But I think wiring in a new socket is preferable anyway, once I get around to it... – Codemonkey Apr 14 '20 at 08:30
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To Avoid Fire

As noted in other answers and comments, there are issues related to wire size and length that can cause overheating if not appropriately dealt with, and the issue of waterproofing the connection, both that can lead to shorts and fires.

So You and Your Family and Your Friends Don't Die

A person, just out of the hot tub, is covered with water, walking around dripping it on the ground, it's pooling in to puddles, their barefoot (who wears shoes in a hot tub?), they're in the UK where power is 240v and likes to really mess things up if shocked, AND then let's effectively put an outlet and plug on the ground nearby in the form of a cord to extension cord connection. It's as if someone just got out of the shower and then throws water at the wall socket and then puts both hands all over the wall. Sooner or later, it simply a matter of time, someone is going to get a major shock, or worse, electrocuted.

Related, recall how smart and vigil we are, and think how much is the same for the average person, then recall that half the people in the world are below average, and that the instructions are written for everyone, not just us.

They make those statements as a CYA yes, but also a COA (Our in place of Your) because we really do need protecting from ourselves, at least some of us do. It's very likely a government mandated item that the instructions note not to use the extension cord.

Ack
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    um, the OP states in the question that the plug and cord connection will be inside of a building like 20' away from the spa... – Jimmy Fix-it Apr 07 '20 at 20:50
  • @JimmyFix-it yet, the OP asked this as well: "WHY not to use it with an extension cord. I wonder if it's to do with the risk of having such connections outside in the elements?" – Ack Apr 07 '20 at 22:01
  • If there's any damage to the cable, you and your family are still going to be toasty critters, with or without an extension cable. That's why we have RCDs, and RCDs make this answer irrelevant The instructions are simply wrong - they should say to use an RCD instead, and then the whole extension cable thing doesn't matter. – Graham Apr 08 '20 at 11:52
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    ... In the UK, wiring regs for some time have required all sockets to go through an RCD for new installs. With or without that though, plug-in RCDs have been cheaply available for over 30 years, and all advice for that time has been to use one on every outdoors electrical appliance. Anyone using a hot tub without an RCD is frankly too stupid to deserve to live. – Graham Apr 08 '20 at 11:53
  • FWIW @Graham the hot tub cord has an RCA built in, and I think I read that there's another one in the unit as well. Obviously a good idea to add ANOTHER one at the socket as well. I had thought my distribution box had RCA circuits in it but on closer inspection I see it's just regular fuses, so I'll get one for that. – Codemonkey Apr 08 '20 at 13:16
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    @Codemonkey Fair enough - if there's one in the cable to the tub, that explains why they don't want extra extension cables. As you say though, if you do have an extension cable then you want something to cover that. For myself, plug RCDs are cheap enough that it's a no-brainer to put them on anything which connects to outdoors, just on general principle. Just by the way, we do have a hot tub, and we do have an extension cable, but that extension has an IP67-rated enclosure round the soocket and it's hung off the ground with drip loops on the cables. And an RCD indoors, of course. – Graham Apr 08 '20 at 13:37
2

Depends on the current requirement of the tub

Your tub will likely have a label that specifies the rated current draw and/or rated power. If only power is stated, divide Watts by RMS voltage (220V) to get amps required. You mention using a 13A cord - comparing to the rated draw of the tub is necessary to determine if this cord is up for it.

The adequacy of the 13A cord will probably turn on whether your tub is electrically heated. Some tubs have gas or propane heating, and others heat electrically. An electrically heated tub would undoubtedly require much more amperage.

This is in addition to the other very valid considerations already mentioned.

Mike Thielvoldt
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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know the details of contributing here. – Daniel Griscom Apr 08 '20 at 13:13
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Earthing protection is an important consideration. You cannot have a situation where you may not be earthed...even temporarily.

Raj Shah
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    UK power plugs (and many others) are designed in a way that when you plug them you get the earth first and then the power. When unplugged, you lose first the power and then the earth. It is the same on the extension cord. – fraxinus Apr 08 '20 at 09:49
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In the EU-style consumer power grids (220-240v, separate ground) these marks "don't use extension cords" are put on all appliances that draw 1kW or more. AFAICRecall, every space heater has it.

I don't know the reason, but it has to do something with the risk of overloading a single outlet (~3.5kW) by plugging few heavy loads into it. The most probable outcome of overloading is usually a tripped breaker, but sometimes the breaker allows for some tolerance and contacts or cables overheat.

IMHO, if you use a good extension cord and promise not to plug a total of more than 3.5kW, you are OK. Avoid using a cord longer than you need, avoid covering the cable w/ carpets or likes.

And for sure, avoid water near the plugs.

fraxinus
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