In a recent pressure washer thread THM mentioned that you shouldn't use "mickey mouse" leads with induction motors, only I wasn't quite sure what makes a lead become "mickey mouse" category.
Are all tools with induction motors affected or is it only a problem for hungry, high-watts motors, like those in pressure washers?
I was thinking 1.25mm^2 CSA flex is rated for 13A, so you might think it would be ok for any 13A appliance but is it the case that once the lead is so long, you have to upgrade the CSA to avoid a voltage drop?
Is this like the "taking electricity outdoors" considerations where a long cable results in voltage drop? Is it the voltage that upsets the induction motor, or is it something else all together?
Is another problem that above a certain CSA you cannot fit the lead into a plug? Other threads have suggested using "caravan leads" with the big round blue plugs (sorry I don't remember the real name for these) but OTOH don't these have to have a standard plug on one end, so you'll still come up against the same problem eventually.
Induction motors and extension leads arent a particular issue unless the motor is running a compressor, such as in a fridge, and the extension lead is very long and thin. Yes, there's a lot more could be written on this.
My extension lead uses 2.5mm^2 arctic flex in blue. It was a job to terminate. I had to take one of the teeth out of the MK safetyplug to get the cable in, but the flexgrip is still 100% solid. Other brands may vary.
Domestic plugs are generally limited to 1.5mm CSA. You can get a few plugs that take 2.5mm CSA, but unless you plan on some vast length with 3120W it is simply unnecessary.
Ceeform, BS4343, 16A 32A 63A 125A.
Beware these have certain min cable size restrictions for sealing - a thin PVC flex on an appliance may not seal at the cord grip so whilst the plug may be IP44 or IP67, water running back down the flex might be somewhat shocking :-) Under BS7671 a 16A BS4343 should use 2.5mm flex, which has a rather substantial overall diameter compared to most appliance flex which has very small overall diameter 1.0mm flex.
Arctic flex is not actually made to a BS-number, most heavy duty extension leads are based around H0RNF (often miss-named HO7RNF on Ebay) which is commonly available in 1.5mm quite cheaply (64-77p/metre including VAT).
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carry H07RNF and
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has many listings for HO7RNF (lots of cut lengths, no connection just used a couple of the sellers and the cable is very good). Trading Depot do 1.5mm Arctic flex quite cheaply in cut lengths (41p/m) and postage is quite low. Many other suppliers out there, TLC Direct do various black rubber cables, Screwfix probably do "something cheap" on a 25m reel with free shipping possible if you want other stuff.
Most IP rated sockets do have screw-holes in a separate compartment to the electrical components, so can be used "loose", but a common problem is they may not close over a moulded-on plug.
You can pickup ready made IPx4+ rated extension leads in orange, the socket does close over a moulded in plug and everything is moulded, pre-tested etc. I think Homebase did some, also Wickes. Can not recall the brand name.
A large commercial pressure washer could have a 3.1kw induction motor, so is right in the limit for a 13 amp fuse.
IME yes, long leads cause fuses to blow and TOL's to trip. Coiled leads do it as well.
Someone will be along in a minute with the technical bits.
Strange, having been brought up on pressure washers, I now look on extension leads from that viewpoint. Nearly didn't buy one recently because it would only handle 10 amps - more than enough for any power tool I own - but not much good for a HPC.
Ahh, but a 13 amp fuse doesnt blow until around 26A.
Voltage drop will cause a bigger amperage to be drawn. If it is on the limit at 13 amps at the plug, going 25 or 30 metres away to the socket will likely give a 10 volts or so voltage drop. Amps x volts = watts. The motor will always want (say) 2850w, that equates to 12.4A at 230V. With a 10v voltage drop, the current will be going up to 12.95A, so pretty close to the rated limit of the cable. At that amperage, the cable will be getting warm, as although they are supposedly passed for 13A, I'd say the majority of extension leads were not made compliant to the ones sent for testing, so I'd always err on the safe side, and take 10% off of the rated current limit to stay safe.
I've not got the details for flex, but for 3 core cable, 1.5mm sq can carry up to 22A if in free air. The voltage drop for this cable will be 29mV/A/m . If using a 25m extension lead, that'd be .029x12.4Ax25 = 8.99v Voltage drop. For fixed wiring, this would be acceptable - 5% limit on voltage drop,
8.99v is around 4% drop. I have not got any details on flexible connectors, so cannot comment if this is acceptable. I know putting 4 appliances into a 50metre socket is not a good idea, unless they are low current drawers.
Its the high currents that matter more. Some of the top end domestic pressure washers will be right on the 13A limit.
Yup, induction motors are a little unusual in the sense that if you drop the voltage, let them spin up and then apply maximum mechanical load (i.e. much like a pressure washer), they will try and develop the same output power regardless. This means at reduced volts they suck more amps. More amps means more heat to dissipate in the motor windings and can result in damage to the motor. (it also obviously heats the cable more, raises its resistance further and it then drops more volts)
What distance and what size motor are we talking about here?
5% and 13A is all no problem. Today's mains motors are desgined to run at much lower voltage and still be in spec.
13A is a continuous rating at which all marketed goods are legally required to be safe. 13A is in no way a problem - though of course there are plugs that cant do 13A, but nor can they do 12.5.
You should have bought a CEEform plug/connector and terminated the
2.5mm2 on the CEEform plug. You should then have made a short 13A plug to CEEform connector with a piece of 1.25mm2 or 1.5mm2 flex.
13A plugs are not designed to take 2.5mm2 flex and you shouldn't really try to force the issue. Strictly "bush-league" as they say ;-)
Only if it's a crap old-style design. Most decent modern brands of 16A Ceeforms either have a clutch strain relief or (if they have the older style with two bits of plastic and two screws) will clamp down on 1.5mm2 cable no problem. Even if you have an old style Ceeform that is too small for 1.5mm2, you can always use a bit of extra cable sheath to pack out the cord grip.
so whilst
Only for caravan connections afaics. Do you have any other references, apart from table 721?
Table 4F3A rates 1.5mm2 at 16A and the entertainment industry routinely uses Ceeform extensions made up with 1.5mm2 cable.
which has a rather substantial overall diameter compared to most
BS6500?
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heavy duty
Que? Is this a typo?
H07RN-F is the correct designation. The "0" is a zero.
Clipsal 56 series 56P313 with suffix GY for Grey or OR for chemical resistant ORange.
BS1363/A "tough duty" plug terminals may take 2.5mm conductors, but the cord grip will rarely accommodate a 2.5mm cable's outer diameter. You might get Arctic 2.5mm to clamp satisfactory, but 2.5mm H07RNF has quite a wide outer diameter range and may prove impossible with most cord grip designs.
Conversely the Clipsal 56 series plug has a rear cable entry based around an M20 cable gland - so even 2.5mm H07RNF can be accommodated (although I recall quite a bit more tightening is required to get the gland's O-ring to bottom and seal). Unfortunately a downside of the design is that it imposes quite a large min cable diameter, 1.0mm cable typically used on hedge-trimmers & mid-range pressure washers will not seal adequately (7.2-8.5mm). A clipsal compatible solution for small appliance cables is to use the older PDL series plugs - their double-grommet seal on the plug will tolerate very small diameter cable, but at the expense of not accepting anything above
1.0mm 2-core H07RNF.
That is unlikely to seal sufficiently. Geweiss Ceeform IP67 will not seal on 1.0mm 2-core or 1.0mm 3-core PVC cable (that is to say 7-8mm o.d. cable), there were two other equally nasty makes at the bargain basement end of the market.
"Should" was too strong a word. BS7671 regulation reference is indeed
721 & specific to caravans, there was a HSE article recommending
2.5mm, although that may be typo, error or journalistic licence (they do not have to pay for the cable).
Indeed, the installed base is vast - 1.25mm routinely 13A, 1.50mm routinely 16A.
Firstly it may be generally made to, but not tested to, which are quite different things. Secondly as I was typing I was trying to recall Cole's article, HSE comments, Prysmian comments and a comment from one committee report.
Found it. If you go the IET forum and search under "Flexible cable type H07RN-F (BS 7919)" you can read responses to Mark Cole's article.
BS6500 is for domestic & similar environments, down to +5oC. BS7919 is for industrial environments, down to -25oC. The problem centres around mechanical robustness of Arctic PVC in commercial environments at LV. It is true that there is a bias to phase out PVC (that I know that from one Prysmian engineer and one AEI engineer), probably because no- one is making enough profit on it (ooops, typo!).
Quite a few yellow arctic cables have had no BS number and are more blue-brown than yellow along their length as the sheath is so thin, there is quite a lot of variation. Stuff branded is a different matter and seems fine.
Deliberately :-) If you Google use H07RN (zero, re "07"). If you Ebay use HO7 (letter O, incorrectly).
Ironically people miss-searching for HO7 may have forced sellers to list as HO7 as well as H07 via Ebay's "keyword auto-suggestion" :-) Seen the same thing on part numbers, special characters and miss- spellings which can often work in your favour. Ebay used to miss 16mm2 where the 2 was proper superscript for example, not checked if it still does; meant you could pick up 100m of 16mm 6491X for 99p plus =A38.50 delivery or similar nonsense.
If assembling a lead for pressure-washer applications, just make sure the cable glands do in fact seal - make up, hose spray whilst dead, diss-assemble and examine for water ingress. I found a lot did not seal properly. A pressure washer creates a water jet way up the IP scale, such that moulded extension leads may be preferable. I found very deep embossed lettering on a cable sheath situated under a cable gland can cause water migration under simple hose spraying. To survive a direct blast from a pressure washer is probably IPx8 rating due to the pressures involved.
Bricklayer was using his cement mixer & angle grinder off one of those plastic wind up extension lead cases. .... later in day noticed case was so hot it had all melted and deformed ....... obviously did not believe the label that said unwind fully before use.
OK, that's part of a proprietary waterproof plug/socket/connector system. I was thinking of an ordinary 13A plug. I dare say you could squeeze 2.5mm2 into a Lewden weathertight plug as well.
OK, I was thinking more about strain relief than weather sealing. I think I see a pattern here...
MK "Safetyplugs" with the captive nut clamp, rather than the tiny little screw, used to be really useful for doing this. They also loosen less if there is any heating of the clamp screw.
Lewden are somewhat better built than Clipsal too. I think Clipsal might have revised their plug rear gland design in Australia to ensure better sealing over a wider cable range (pretty much like the recent BS4343 connectors as you point out).
The benefit of Clipsal 56 series is their modular approach - you just choose how many backbox ways you want re 1-9 and populate with sockets, lids, switches, RCD enclosures, anything. Price can be outrageous of course.
MK Masterseal tried to be "modular" with their box-couplers, but on uneven walls the very short couplers can simply pull out - requiring a levelled backplate or conduit fittings. Masterseal lacked a 1G+1G or 1G
+1G+1G moulded backbox, although that would still require levelling of the screws or the thinwall polycarbonate boxes can distort possibly compromising the seals. Masterseal Compact might solve the problem of plugs with moulded cord grips (eg, pressure washer) not fitting sockets, but I have never checked.
Pressure washers are unique in producing very high pressure directed spray, which defeats many conventional seals at close quarters. Moulded waterproof extension leads actually might have the edge over DIY if they can handle the moulded cord grip.
Yes, but before voltage drop becomes a problem, the fault current loop resistance becomes a problem.
For a 13A extension leads, you should stick to the following max lengths based on CSA, and never daisy-chain multiple leads:
1.25mm² - 12m
1.5mm² - 15m
2.5mm² - 25m (cable won't normally fit in 13A plugs) Spot the pattern - it's easy to remember.
You can increase the length proportionally with a reduction in the fuse in the extension lead plug, so with a 5A fuse, 1.25mm² lead can be 12*13/5 = 31m long.
In theory you could increase the lengths if you know the lead is always going to be RCD protected, but you can't really know that to be the case, give that extension leads are inherently portable.
Now I'm wondering what this definition of a problem is based on.
15m of 1.5mm=B2 will drop 4.4v at 13A and have a PSCC of 700A.
700A opens even a D type breaker in 0.001-2 seconds, well within 17th edn socket disconnection times.
There are 13 Amp cables that can take the current intermittently and those that can take it 24/7. I have one of each, but if I am using my arc welder, I chose the thicker one.
If the cable is on a reel then totally uncoil it, or it will melt.
The figures Andrew quoted are in the IET code of practice for in-service inspection and testing ('PAT testing' if you must call it that).
That's an optimistic figure. It's more like 5.6 V at 70 deg. conductor temp.
Bzzt - only for zero source impedance at the feeding end! In reality you can have an ohm or more of Zs at the socket that the extension is plugged into - and possibly over 2 ohms if it's on a 20 A radial circuit. The 15 m extension adds another 0.4 ohm or so, giving a worst-case overall Zs nearer to 2.7 ohms (85 A fault current).
The operating time of the 13 A plug fuse is more relevant. Looking at BS 1362, about 90 A is required to clear a 13 A fuse in 0.4 s. Convinced now?
Exactly, a code of practice does not equal a problem.
Sure, I was being a bit handwavey there.
I dont see 0.4s clearance in worst case scenario as being a genuine problem. 1-30 seconds clearance for type B 32A breaker would be, but as you point out the 13A fuse would go first in this case.
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