PAT / ITEE Testing. IEC lead fuses

[christopherelston12@]

Hello all.

I've recently qualified as a PAT tester with C&G. First post on here, so please go easy - all advice and feedback gratefully received!

I was testing a computer monitor in my office (fairly modern LCD type - very low power draw of between 29w and 72w according to the manual). The IEC lead with it has a 13A non-rewireable plug rating with a 13A fuse installed, but then has a 10A rated connector on the C13 connector. It is hard to tell if this is the one supplied by the manufacturer, but let's say that it was. The CSA of the cable is 0.75mm and so the 13A fuse meets with what's acceptable from the ITEE 5th edition table (10.6 pg80), but the connector being stamped with 10A has me confused, as well as the fact this cable is paired with such a low power draw device where a 3A fuse should be more than sufficient.

So to the purpose of my post: Is it advisable to replace the 13A fuse with a 3A fuse in this IEC lead to add additional protection to the monitor & cable? Granted, the fuse is to protect the cable and not the device I know, but I still wondered amongst you experienced testers out there, what would you do here? Should I leave the fuse as is, or swap it out for a more appropriate 3A fuse?

Many thanks in advance.

 

[ericmark]

I would swap for a 3 amp, as you point out, only rated at 10 amps, but fig of 8 plug rated at 2.5 amps, and I would not worry about fitting a 3 amp fuse in that, so can't really say must be swapped, it is up to you. This

Lists the connectors and the C15A and C16A are the standard used with kettles, so one can hardly fit them with 10 amp fuses, so would not worry too much.

 

[JameZZ]

Ideally should have a 5A in, but very common for IEC leads to have a 13A in the plug. In reality very unlikely to become overloaded in an office environment but possible.


It's great your checking the fuse though, 99% would not.

 

[EFLImpudence]

I thought appliance flex was subject to different regulations - not BS7671.

 

[ericmark]

I often wonder about PAT testing, or the inspection and testing of in service electrical equipment. It this one item ? It is portable. The one I worked on came in one 22 articulated wagon loads.

I had to attend a good deal of health and safety lecturers, and we would be told things like we should not use any equipment which does not have a PAT test label, and taking pleasure to show how he should not use the TV he was using to assist his lecturer as the power leads had no label.

Some common sense needs to be used, so you have a lead

and really you have no idea of the cable size, the advert with this picture said

so this lead designed for 5 amp it seems. I know in my house I have loads of these lead sets, and also fig of 8 leads

and they swap what being used with many times. c7/c8 and they as said rated at 2.5 amp. There is often a clue, this one says 10 amp. But I would carry two fuses, 3A and 13A, I know there are 1, 5, 7, and 10 amp as well, but I don't carry them around with me.

 

[JohnW2]

I thought appliance flex was subject to different regulations - not BS7671.

I think/thought the same - but who (other than yourself) has said anything about BS 7671 ?

 

[christopherelston12@]

Ideally should have a 5A in, but very common for IEC leads to have a 13A in the plug. In reality very unlikely to become overloaded in an office environment but possible.


It's great your checking the fuse though, 99% would not.

Hi JameZZ, thanks for replying.

So can I double check with you: in a cable with a moulded plug with a clear 13A/250v stamp on it, it is fine to put a 5A (or 3A) fuse in that cable based on it's current usage with an LCD monitor as the 5A/3A would not be larger than the stated fuse rating (of 13A) for the cable. There is no risk of any overheating or complexities such as that with doing this is there.....? I guess if that particular IEC lead were then accidentally moved to plug into a high power draw device, like an old kettle (without a base), then the fuse should blow, but that's all. Although I know in terms of basic physics it seems like the 'right' thing to do to swap out the fuse for the most appropriate rating, but I don't want to be creating a potentially problematic/dangerous situation through good will if that makes sense!

I feel like this aspect relating to fusing wasn't gone into much, if any, detail on the Level 3 course I did!!

 

[ericmark]

I have one with the Schuko plug

so 16 amp, so would not really worry with 13 amp. The point is you are testing the lead, not the equipment it powers, and the lead can move around, that why we test them independent of the equipment.

 

[plugwash]

I thought appliance flex was subject to different regulations - not BS7671.

The majority of the world, heck even the majority of Europe does not have plug fuses so international standards are going to be written as-if they did not exist.

As I understand it. There are standard current ratings for flex which seem to be the same across many IEC and IEC-derived standards* including BS7671.

0.5mm² - 3A
0.75mm² - 6A
1.0mm² - 10A
1.5mm² - 16A

A rating of 13A is also quoted for 1.25mm² flex, but that one seems to be a UK oddity.

In general, the minimum flex size for appliances with fixed cords is determined by the current draw of the appliance. Appliance designers are expected to select a flex size based on the power draw of the appliance. Presumably this all works on the principle that "overloading is unlikely" and that "if the circuit passes fault protection requirements a short flex hung off the circuit probably will too".

For removable power cords, my understanding is that the minimum flex size is determined by the current rating of the appliance input connector. However, there is a dispensation for short power cords. Short (I forgot the max length but I think it's something like 2m or 3m) cords with 10A connectors are allowed to be produced with 0.75mm² flex and short cords with 16A connectors are allowed to be produced with 1.0mm² flex.

I suspect this dispensation was driven by lobbying from manufacturers. At the end of the day every standard is a compromise between cost and safety. Presumably the combination of the fact that flex current ratings are quite conservative, that short flexes are less likely to see adverse thermal environments, and that few appliances with 10A inlets actually use anything like 10A, particularly when used on 230V supplies.

Where the whole "overloading is unlikely" thing starts to fall apart is if equipment has pass-through power outlets or if users start using splitters or adapters. I don't think there is any formal standard for such splitters and adapters, and even if there was there is no way it could prevent all the possibilities for creative misuse. Mind you, in many countries the same applies to normal extension leads.

Which leaves the whole question of what fuse should be fitted. I can certainly see an argument for "fuses should be no bigger than needed", but also the argument that the majority of the world gets on fine without having plug fuses at all.

* The yanks have their own completely different system of cable sizes and ratings.

 

[Ragnar_AT]

Many countries using CEE 7 plugs require sockets to be protected at no more than 16 A and all extension leads to be rated at 16 A, so no amount of creative splitting could cause an overload beyond the trip curve of the MCB. There is one exception, power strips with no more than four CEE 7/16 sockets (2.5 A each) may be fitted with 0.75 mm2 flex not exceeding a certain length.
France and Belgium allow for 20 A protection but seem to assume that the risk of overloading extension leads and power strips is small enough to be acceptable.

 

[hllns]

These days IT equipment that has a higher power draw usually come either with C16 or even C20 inlets, the cables for this are usually 1.0mm2 or even 1.5mm2 and you can't just use your 0.75mm lead in unless you're using an adapter or using it to feed a PDU.

It's a bit of a pain for us as the spare PSUs don't come with a lead in the box so we've been having to buy job lots of 13A plug to C15 leads.

 

[opps]

Hi JameZZ, thanks for replying.

So can I double check with you: in a cable with a moulded plug with a clear 13A/250v stamp on it, it is fine to put a 5A (or 3A) fuse in that cable based on it's current usage with an LCD monitor as the 5A/3A would not be larger than the stated fuse rating (of 13A) for the cable. There is no risk of any overheating or complexities such as that with doing this is there.....? I guess if that particular IEC lead were then accidentally moved to plug into a high power draw device, like an old kettle (without a base), then the fuse should blow, but that's all. Although I know in terms of basic physics it seems like the 'right' thing to do to swap out the fuse for the most appropriate rating, but I don't want to be creating a potentially problematic/dangerous situation through good will if that makes sense!

I feel like this aspect relating to fusing wasn't gone into much, if any, detail on the Level 3 course I did!!

*I am not an electrician*

Why not put a 10amp fuse in it? Granted they are less common than 3/5/13 but they do exist. That way if it is used for something else, you won't need to worry about the fuse blowing.

My Festool CT-SYS dust extractor has a 5m C13 flex. The motor is 1000w and the max rating for connected tools is 1200w. I have a sneaking suspicion that the fuse is rated at 13amps. Will check it later. I do have some 10amp fuses but to be honest, if it does have a 13amp fuse I will leave it as is.

Best of luck, and thank you for asking the question. Us non-electricians learn form the responses to questions like yours.

 

[333rocky333]

You say the connecter is rated at 10a but no mention of the plug rating, most moulded plugs have a rating embossed on them, usually 5a or 10a and occasionally 13a.
1 would not expect the fitted fuse to exceed the plugs rating.
As for your suggestion a lower rated fused lead might get used for a kettle.
The fuse would likely get warm but I would not expect the fuse would actually blow in such short time of a kettle operating.

 

[christopherelston12@]

You say the connecter is rated at 10a but no mention of the plug rating, most moulded plugs have a rating embossed on them, usually 5a or 10a and occasionally 13a.
1 would not expect the fitted fuse to exceed the plugs rating.
As for your suggestion a lower rated fused lead might get used for a kettle.
The fuse would likely get warm but I would not expect the fuse would actually blow in such short time of a kettle operating.

Hey, thanks for the response.

The cable in question is a moulded plug embossed with 13A/250V text on the plug. The C13 connector at the other end is embossed with 10A /250V text. The moulded plug has a 13A fuse in it, which is why I wanted to check people's experience of this scenario. This cable has been in use for years in my home office and I've never noticed it ever get warm and the fuse has never blown etc. My concern, if I am to proceed to employment in PAT testing in public, that when faced with an anomaly such as this, is it best to change the fuse to the lowest rated marking on the cable, (in this case 10A) or focus on the power draw of the equipment it is connected to....? This cable is connected to an LCD monitor, which in this case would only need a 3A fuse max as it has a tiny power draw, but I know the fuse in the plug is to protect the cable, not the equipment.

Any further thoughts you have on that would be appreciated.

Thanks again

 

[JameZZ]

The C13 IEC is rated at 10A. If the cable was 0.75mm I would put a 5A fuse in the plug, if the cable was 1.00mm I would put a 10A in if I had one, or a 5A.

It’s very unlikely any equipment that has a C13 fitted to it would draw anywhere near 5A, the only issue would be if the equipment had a high inrush current which could blow a lower amperage fuse, such as a vacuum cleaner.

As others have said your testing the cable, and the fuse is there to protect the cable. Also as others have said, its common in other countries to have a 16A unfused plug on the other end.

In an office environment, the C13 is extremely unlikely to be overloaded. Higher chance in an AV environment (a theatre for example) where the use of daisy chaining IEC appliances and the use of IEC splitters are used.

Apologies for my cynicism and to generalise, but in my experience PAT testers don't check the fuse, the cable condition or whether the CE mark on something is genuine, and most companies that procure PAT testing services are box ticking and want it done as cheaply and quickly as possible creating a race to the bottom (as is with electrical work in general). So it’s great you are taking such care but I wouldn't overthink it too much.