PAT testing problem ( need help please )

[VasMasta]

i am a bit of a newb at it and its been about 5 years since i did my course.

I have been doing some PAT testing and came to a problem

this old fan heaters have 55W power but fitted with 5Amp fuses
in my understanding anything below 700W must have 3Amp fuse, is that correct ? there also about 5+ power tools that rated at less then 700W have 5-10-13 amps fuses.

i am confused and dont know what to do here... why do they have this fuses ? should i change them to 3amp? i am paranoid to do something wrong here.

Please any help much appreciated

 

[Marvo]

this old fan heaters have 55W power but fitted with 5Amp fuses

This doesn't sound right, are you sure that it's not just the actual fan motor that's 55 watts? A 55 watt heater isn't going to produce much heat....

 

[telectrix]

power tools will need bigger fuses than what equates to the rated power, due to start-up current. same with fridges. you have to make a judgement based on the cable size, type of load, and manufacturers recommendation ( if available).

 

[VasMasta]

Marvo thats what it said on the heater 55W i am not sure maybe i missed something...

telectrix that helps cheers mate.

I just dont want to get in trouble for putting PAT testing PASS label with wrong fuse on it.

all i was asked to do is some PAT testing at this big work place because i did a course long time ago and have a certificate. I did my visual and insulation/earth test fine. I didn't want all this headache with fuses...

 

[Deleted member 72666]

As Marvo has said it's highly unlikely that a mains operated fan heater is rated so low, you can check its resistance and by using ohms law you can fuse it accordingly.
Are you sure it's a heater and not just an old desk fan?

 

[Lucien Nunes]

this old fan heaters have 55W power

As mentioned above, if it's an ordinary general purpose heater this can't be right. A fresh cup of tea gives off more than 55W of heat! Most heaters are 1000W and up, small background heaters might be a few hundred watts.

in my understanding anything below 700W must have 3Amp fuse, is that correct ?

No, not really. In general, modern appliances will have suitable fusing internally to protect the appliance, the plug fuse is mainly to protect the flex. Anything with 0.5mm² flex should have a 3A fuse and in theory anything else made to the relevant standard could have a 13A fuse regardless of the power rating, unless the manufacturer states otherwise. The COP recommends 3A for anything less than 700W but clearly there are situations where this is applicable and others where it doesn't work. I like to fuse down to the minimum where there's definitely no disadvantage to do so, e.g. table lamps and small electronic goods all get a 3A. Computers and similar devices with SMPSUs get a minimum of 5A because of the inrush, and the COP recognises this.

5A and 10A fuses are useful for protecting removable power cords that could be overloaded, e.g. A 6A rated IEC cord could be overloaded if fitted with a 13A fuse and fed into an unfused splitter block. Therefore you will often find 5A or 10A fuses in plugs on these, according to cable rating.

As Tel points out, if you put a 3A fuse in a 100W fridge it will blow immediately at startup, a 13A fuse is correct and safe, because the fridge motor contains its own overload protection. The same is true of many other motorised appliances.

 

[VasMasta]

As mentioned above, if it's an ordinary general purpose heater this can't be right. A fresh cup of tea gives off more than 55W of heat! Most heaters are 1000W and up, small background heaters might be a few hundred watts.



No, not really. In general, modern appliances will have suitable fusing internally to protect the appliance, the plug fuse is mainly to protect the flex. Anything with 0.5mm² flex should have a 3A fuse and in theory anything else made to the relevant standard could have a 13A fuse regardless of the power rating, unless the manufacturer states otherwise. The COP recommends 3A for anything less than 700W but clearly there are situations where this is applicable and others where it doesn't work. I like to fuse down to the minimum where there's definitely no disadvantage to do so, e.g. table lamps and small electronic goods all get a 3A. Computers and similar devices with SMPSUs get a minimum of 5A because of the inrush, and the COP recognises this.

5A and 10A fuses are useful for protecting removable power cords that could be overloaded, e.g. A 6A rated IEC cord could be overloaded if fitted with a 13A fuse and fed into an unfused splitter block. Therefore you will often find 5A or 10A fuses in plugs on these, according to cable rating.

As Tel points out, if you put a 3A fuse in a 100W fridge it will blow immediately at startup, a 13A fuse is correct and safe, because the fridge motor contains its own overload protection. The same is true of many other motorised appliances.

thx for your help ! i have better understanding about this stuff now


cheers guys

 

[Darkwood]

This is all explained on your PA-Testing course and as lucien points out you have to understand the item you are testing - sometimes its there for over current of the appliance, sometimes overcurrent of the flex and sometimes just to give S/C protection to the reduced sized cabling of the appliance...

Some appliance will be classed as fixed load thus the fuse only needs to be fitted as the plug top requires one to plug into a ring main and a fuse over rating the flexes ccc is not a concern.

You don't require to hold a PA-Testing Cert' but not doing so could be a costly if anyone is injured or killed and you are required to prove your competence. I assume you don't hold the cert by the nature of the question?

 

[Chrisuk]

I am a trainee so be gentle, I know 55W is not high at all but as u all know 230V/5=46ohms 230V/46ohms = 5A that's what's in it
Also i thought P/V=I?? But if i do that i get .23A (yeah I know I probably should be in the trainee!! u would probably keep warmer by rubbing your hands together to generate heat than what that's giving out ha

 

[Darkwood]

Its likely the OP missed a zero off the 55 thus 550w - you have a standard 500watt heating element and 50 watt taken by the fan.

 

[Chrisuk]

So 550W/230V=2.39A, so if it is 550 and not 55 he can use a 3A fuse instead of the 5A??

 

[Darkwood]

The motor for the fan will have an inductive nature and the inrush on power up may require the next size fuse up... this is why you often see a fridge with a 0.75 or 1mm flex covered by a 13amp fuse which actually overrates the flexes current carrying capacity... as the loads are classed as fixed and usually will have added protection that a thermal trip the 13amp fuse doesn't need to protect the flex from overload situations.

On paper you are correct but in the real world its not as simple as just calculating the load and slapping the next size fuse in... many factors in design and working can mean the fuse may seem to be incorrect this is why these PAT 1day wonder courses are not worth the cert' you get at the end - i did one and had several questions for the teacher that he couldn't respond to with a good reply so i said in essence all thosein this class today without any indepth electrical background will be making incorrect observations regarding the points i made yet your going to pass them a paper saying they are trained.... his reply was '' If we are going to get scrutinised all day from me no-one will pass with all my interruptions " I just said so im right its just a money making scam that does not prepare you for the real world..... surprised i passed TBH thought they were going to fail me on purpose lol...

 

[Chrisuk]

That makes a lot of sense that different factors will come into play changing the size of fuse rather than just working it out, is this what comes with real world experience or does the onsite guide or BGB have tables for this??
I'm doing my 2365 over years and just came from the Electrical Trainee thread a moment ago, seems you can get a qualification for so much now in a very little time if u have deep pockets, not sure how good someone would be though, after 5 weeks become a sparky yet I'm told at the end of level 3 I WON'T be one, I need NVQ3 real world experience!!yet they do it within weeks! It's all about the ££££££££

 

[Darkwood]

Its not really written down in depth it comes with experiences so really you should be working under someone with guidance or pick it up from yrs in the trade... deffo' not walking into a 1day course to PAT test without any background or knowledge.... the amount of passed equipment ive found with incorrect flex for the environment etc ..... it keeps me in work though sorting all this crap out so can't rant too much.