3kw Immersion blowing sfcu 13a fuse about once a month...any ideas?

[bleach]

On dedicated 16amp mcb Wired in 2.5t&e to sfcu (13a fuse) then 2.5mm heat resistant flex. Fuse has popped twice in last 8 weeks etc. Element R 18ohms. all seems ok? Should I just swap sfcu for 20amp double pole switch? haven't clamped to measure the draw yet as didn't have it with me.

Cheers

 

[dazza1981]

I think 17 to 18 ohms is about right for the element...... as you say clamp it and see what its pulling or just change to a 20 Amp double pole switch.
2.5mm is protected sufficiently by the 16 Amp breaker !!

 

[Plonker 3]

What is the Kw rating of the heater?

 

[dazza1981]

What is the Kw rating of the heater?

the title says 3 kw

 

[telectrix]

fit the 20A D/P switch. cable is protected by the MCB.

 

[Guest77]

Test between the pins of the element and the outer case of the element to ensure there is no continuity, sometimes it needs to get hot before it will expand and touch the outer case causing a fuse to blow, it can happen and may have a fault.

 

[bleach]

Thanks mdj, didn't know that. Guess its a possibility.

Thanks Tel. I will swap for 20amp dp switch as u say.

 

[UKMeterman]

Two ideas;
1. Go and perform a 500V insulation test between N and E.
2. Check to make sure there is no clothes or other insulating materials around the fused spur unit?

 

[Plonker 3]

Two ideas;
1. Go and perform a 500V insulation test between N and E.
2. Check to make sure there is no clothes or other insulating materials around the fused spur unit?

What???????

 

[dazza1981]

What???????

Dill not just me then mate !!!!

 

[UKMeterman]

Yes,
The 500V insulation test to try to see if there is any fault with the element.
2. 3Kw is right on the upper limit for a 13A fuse link, it is a bit of a long shot but if it is well insulated it could degrade and fail over a long period.

 

[Darkwood]

Clamp meter best way to go, element resistance and Insulation testing can only give guidance as Elements can hide problems when they are cold, the expansion on the metal can create intermittent short circuits or small overloads.

Also check the voltage if its 240 at 18ohms you will get 13.33 amps thus a small overload for very long period more current if less resistance (ohms law).

As mentioned above as long as your flex is rated higher than your clamped current then just put a DP switch on and use your 16amp mcb for cable S/C protection as the nature of the load is deemed to be a fixed load.

 

[Plonker 3]

1 you never said what to carry out the IR test on, what about L-E

2 how many items if clothing would it take to over heat a bs1361 to make it blow? I would say bloody loads, beside don't you think the op would have seen them if they were there?

 

[vxwestie]

You will see this many times with a bit of experience. 13amp 1361 on an immersion will often grow 'tired' over a period of time. Sometimes short periods, sometimes longer ones. It's just not a good idea and you'll always benefit from doing away with them. As has been said, a 20dp switch on a 16a mcb is the way to go.

 

[UKMeterman]

1.
I Did say N-E N is connected to L thought a 18 ohm resistor in this case and bypasses any single phase thermostat.
2. I have come across plugs and sockets in airing cupboards used for the impersion heater and sometimes they have been totaly cooked. If the FCU was of similar poor design then the thermal issues could have pushed it over the edge, particularly if the mains supply voltage was up towards 253.

 

[Chr!s]

1 you never said what to carry out the IR test on, what about L-E

2 how many items if clothing would it take to over heat a bs1361 to make it blow? I would say bloody loads, beside don't you think the op would have seen them if they were there?

the fuse ratings and curves are with an open fuse carrieronce you enclose the fuse this derates. Couple this with a high voltage could cause the fuse to blow.

As a guide most fuse companys as an approx guide tell you to derate the fuse if enclosed by 0.8.

Chris

 

[Chr!s]

1 you never said what to carry out the IR test on, what about L-E

2 how many items if clothing would it take to over heat a bs1361 to make it blow? I would say bloody loads, beside don't you think the op would have seen them if they were there?

the fuse ratings and curves are with an open fuse carrieronce you enclose the fuse this derates. Couple this with a high voltage could cause the fuse to blow.

As a guide most fuse companys as an approx guide tell you to derate the fuse if enclosed by 0.8.

Chris

 

[Besoeker]

On dedicated 16amp mcb Wired in 2.5t&e to sfcu (13a fuse) then 2.5mm heat resistant flex. Fuse has popped twice in last 8 weeks etc. Element R 18ohms. all seems ok? Should I just swap sfcu for 20amp double pole switch? haven't clamped to measure the draw yet as didn't have it with me.

Cheers

3kW and nominal 230V is a bit over 13A.

 

[davesparks]

Generally the 3KW rating will be at 240V, the only thing that changed when they brought in this theoretical 230Volts was that manufacturers started printing the 230V rating on labels in addition to the 240V rating.

 

[Engineer54]

Test between the pins of the element and the outer case of the element to ensure there is no continuity, sometimes it needs to get hot before it will expand and touch the outer case causing a fuse to blow, it can happen and may have a fault.

Yep, this is often also the case with cooker elements too. Such elements can give almost perfect readings when cold, the faults only start to readily appear as they are used and get hot, thus breaking down the insulation!!