upgraded breaker concern

[Artisanian]

First i would like to say HI to you all, recently i was asked to remove a 16amp type D 3 ph breeaker in a heating unit,and replace this with a 20 amp breaker.

I noticed that the cables to the heater elements were showing signs of overheating (black and brittle). i have refused to fit the new breaker. am i right in refusing?

the running current is 10.4 amps and allowing for diversity i feel that the 16 amp should be sufficient. your advice would help.

 

[Doc Hudson]

Welcome to the forum, why were you asked to change the breaker?

Doc H.

 

[Chr!s]

what's the cable rated at taking into account of an relevant de rating?

What sort of heating unit is it?, does it have overload protection?

You say 10.4 amps running current, is there a start up current rating?

Why are you applying diversity?

Are you sure its not the heater causing the damage to the cable?

 

[Andy™]

is the heat damage thoughout the cable, or local to the MCB? what size cable is it? will it meet Zs of new MCB?

 

[Evans Electric]

Must be a starting inrush if its a type D . Are the terminals tight ?

 

[oldtimespark]

Is the unit CE marked if so it might void the CE compliance perhaps netblindpaul could shed more info on the subject

 

[Artisanian]

Hi lads, thanks for the replys, the unit in question is a water,air, curtain.it has got overload protection,there is no start up current only demand current, with a thyristor control (variable)

I applied diversity for the design of the unit being unsure if the label on the unit had taken this into account.

I am unsure if the heater elements are the cause of the burning, as the unit is 13 years old+ but it is the first 6" from the element that has burnt.

I was asked to change the breaker as the origonal keeps tripping.

The cable appears to be about 1.5mm but is of a multi strand heat resistant type and could be 2.5mm, all connections are tight and secure.

I am more interested in the regs concerning this queery(sounds gay)lol

If the breaker keeps tripping surely putting a bigger breaker could cause a fire?

 

[Andy™]

if heat damage is only last 6", then its either a dodgy connection, or heat resistant cable should have been used and wasnt.

i doubt changing MCB is going to fix anything, and i cant see why its a D type either. if its just a heating element then should be fine on a B or C. you really need to find out why the MCB is tripping

 

[Evans Electric]

That sounds like the heat from the elements travelling up the cable , it could do with High temp flex internaly to porcelain connectors then replace flex. As Andy says , a type B would do the job , try your ammeter and choose MCB to suit . Perhaps the Type D is buggered , as we say in the trade. If its a 10A load then a 16A should be OK.

 

[Artisanian]

perhaps i was wrong then to refuse the upgrade! I thought that the breaker was there to protect the conductors,elements,and controls, and signs of burning, be it through overload or heat from the elements should cause the breaker to trip, that being the breakers job.

But surely putting a bigger breaker in, would only allow the overload or overheating to become worst and take longer to trip, This was my concern.

when the wac unit was designed surely they took all these factors into consideration and put the correct breakers,cables etc in place.

All my technical manager wants is for the unit to work and not trip out all the time.

All i want is to repair the thing correctly which will require a lot more time than just replacing breakers.

 

[Lurch]

When is the MCB tripping? Is it at start up, randomly, a set time after start up, something else?

Personally I'd tell your boss to change it himself as it's not how it's done. I'd also refuse to randomly uprate breakers.

 

[muffin]

the appliance sounds old, e.g the breaker that is there at the moment has been fitted for some years. has it worked ok up until now? if so then there is a fault on the appliance and the mcb is doing its job.

you are right to refuse to do it. the idea of uping the mcb might be ok if the heater is brand new but to do it now is clearly the wrong way to go.

reg wise you have a maximum rating the cable can carry. this has to be worked out but generally 1.5=10amp max mcb 2.5=20 amp max mcb. but both will take more, its just a good rule of thumb, it only really changes when its very long runs or run through thermal material like loft insulation ect.

i personally would be removing the supply from the heater phase neutral and earth.

and carrying out an insulation resistance test between all of them, i think you said it was three phase if so measure between the phase on low ohms and if you have any odd reading then you have a faulty element

a 3 kw immersion htr normally have a around 19ohms live to neutral, and should be over range on M ohms live to earth or neutral to earth.

hth andy

 

[Artisanian]

Seems as if he is listening to what i have said, he is now allowing me to diagnose and repair this unit.

I believe the unit has a long history of trouble and was being reset every 2-3 days.

I will check the elements,cables, and thyristor control, will also test heat build up within the unit itself and see if the fan is pushing out enough heat(incase there is a restriction causing heat build up).

Thanks for the input lads.

 

[SPECIAL LOCATION]

Seems as if he is listening to what i have said, he is now allowing me to diagnose and repair this unit.I believe the unit has a long history of trouble and was being reset every 2-3 days.

I will check the elements,cables, and thyristor control, will also test heat build up within the unit itself and see if the fan is pushing out enough heat(incase there is a restriction causing heat build up).

Thanks for the input lads.

Sound like you are now going to be going about the problem the right way!

:Applaud :Applaud:Applaud

Let us know what you find/or not?

Were nosey bu99ers here!!