Could the tank have blown up !

[333rocky333]

Last week was asked to check the blown up isolator switch to an imm element which had been recently fitted by someone else, it was 3 phase and the stat controlled a contacter in the panel in the next room, this Visually looked ok
.
I changed the isolator switch, but luckily tried the stat to make sure it turned the contactor off,
I then found the contacter was welded on.
Checked other contacter and that was the same, although that element was faulty and not in use.

I changed them both, but wondered what could have happened if I had not noticed or they weld shut next time the element goes

The tank had a sort of relief valve on top with an inch copper pipe from it stopping two inch from the floor

The elements were
One 9 kw
One 12kw

 

[Terrywookfit]

Was there no thermal overload on the contactor??

 

[WDIK]

where was this? a school by any chance?

usualy these things are old and open vented.
just a thought the original contactors were they 10a by any chance?

 

[333rocky333]

A well known health centre , which I should not mention
The contactors were 25 a

The biggest element was 12 kw , but when it blew the short circuit KVA welded the contactor in.

We told them to get more suitable contactors

Sorry dont know what you mean by the Thermal cut out bit.
Would that have still worked though as the thing was welded in

The supply was then direct from the 3 phase 16 a mcb via the shorted contactor then through the isolator direct to the element.

 

[WDIK]

overloads are not fitted as its not a balanced load if say one element went down the overload would trip.
each element is by the way made up of 3 elements connected in star and the normal load calcs dont work for 3phs

 

[doitall]

What is the name of the cylinder

 

[333rocky333]

overloads are not fitted as its not a balanced load if say one element went down the overload would trip.
each element is by the way made up of 3 elements connected in star and the normal load calcs dont work for 3phs

Yes it was wired in star, and was as you say 3 elements,
However there has never been a neutral on the star point,
The element tech dept said this is ok.

Although the load was within the contactor, the actual fault current of a dead short would be well in excess.

The tank had Ryco on it but not sure if that was the make