immersion heater supply set up

[glasgospark]

current - 16amp mcb 2.5 radial going through a dp switch 20a which feeds another dp switch 20a which then feeds the two thermostats within immersion ,

i was called because breaker was tripping , immersor pulling 26amps overloading 16amp mcb thus tripping.

immersion system is on the normal side of the supply and not off peak.

i plan on giving immersor two seperate radial feeds , top and bottom thermostats
two seperate spurs and having it on off peak side , there is currently no boost function available.


anyones thoughts

 

[Gazthesparky]

How many immersions are there connected to the 16a supply ? If 2 they are overloading it

Keep it simple do away with one of the DP switches and put a special immersion heater controller on

These are designed for use for 1 supply and have a boost function

 

[glasgospark]

How many immersions are there connected to the 16a supply ? If 2 they are overloading it

Keep it simple do away with one of the DP switches and put a special immersion heater controller on

These are designed for use for 1 supply and have a boost function

1 immersion with 2 cables coming from second dp switch feeding the two stats

 

[Richard Burns]

Logically there cannot be only one immersion heater here, if you have a supply cable going to a thermostat and that is all then there is no control, the thermostat will switch and there is no output. They must be heaters.
A current draw of 26A sounds like two 3kW immersion heaters, presumably top and bottom of a tank (although I may have misunderstood what you mean by immersion).
A 16A MCB will only run for 15 minutes at that loading, so this must have been a recent change over to this arrangement.

The bottom immersion heater should be on its own radial from the off peak supply and generally switched to on so that when the supply comes on it will be on (although if the off peak supply is not independently switched on but only on a time related basis then there should be an immersion timer on it) and the top immersion heater should be on a separate permanent supply with the ability to turn it on for short while to boost the heat if the tank has been drained cold.

 

[glasgospark]

Yes one tank with two thermostats top and bottom .

The set up has been this way since 2008 , can't see how it has only just started to overload , after all it was being switched on every day for hours

 

[Hawkmoon]

Have you IR'd the immersion elements?

If one is down I would go back and recheck my interpretation of the cabling layout -

 

[Edd]

Yes one tank with two thermostats top and bottom .

You say Thermostats top and bottom! Dont you mean I/Heaters top and bottom, which is the normal set up, bottom for main tank ant top for boost.
Ive never seen a I/Heater tank where the thermostat is not part of the heater. A picture would help here.
You also say 2 20A D/P switches why two if theres only one heater?

 

[Hawkmoon]

Is the immersion a top entry (tank) dual type with two stats? like this -
27" Dual Element Dual Stat Immersion Heater | QVS Electrical Wholesalers
This type incorporates two elements, one short (24hr), one long (ec 7) and two stats.

 

[Richard Burns]

Yes one tank with two thermostats top and bottom .

The set up has been this way since 2008 , can't see how it has only just started to overload , after all it was being switched on every day for hours

If it has been running since 2008, and regularly used then I would expect that with both immersions running at the same time it is possible that the top immersion was cutting out before 15 minutes and then the lower immersion was finishing the heating, after a while the MCB has got a bit old and is now tripping just before they get to full temperature.
(still not sure about the thermostat / immersion terminology used)

 

[Gazthesparky]

Is the immersion a top entry (tank) dual type with two stats? like this -
27" Dual Element Dual Stat Immersion Heater | QVS Electrical Wholesalers
This type incorporates two elements, one short (24hr), one long (ec 7) and two stats.

If it is one of these immersion heaters then it has been wired incorrectly and hence causing a fire risk overloading the 16amp mcb

if it is the above heater then it should have a bath/sink switch fitted so that only one heater can be operated at a time otherwise as is happening at the moment the circuit is being overloaded with 2x heaters on it

I would either change the 2x DPs for the bath/sink switch or install an economy 7 immersion timer which is designed to operate on one supply cable by only letting one or the other Immersion on at a time

there's no need to install 2 new circuits just install the timer as this is what it's designed for

 

[glasgospark]

Yeah two immersion heaters I'm calling them thermostats there is top and bottom immersors ,
I was going to make 1 with a boost function and one on the off peak economy 7

 

[Hawkmoon]

If it has been running since 2008, and regularly used then I would expect that with both immersions running at the same time it is possible that the top immersion was cutting out before 15 minutes and then the lower immersion was finishing the heating, after a while the MCB has got a bit old and is now tripping just before they get to full temperature.
(still not sure about the thermostat / immersion terminology used)

Good point but then you are assuming that nobody has ever (in 5 years) run water off at the taps during the heating process - then that 15 mins could end up 30 or more
Can't believe an overload like this would go unnoticed for 5 years - element gotta be down

 

[Gazthesparky]

Yeah two immersion heaters I'm calling them thermostats there is top and bottom immersors ,
I was going to make 1 with a boost function and one on the off peak economy 7

Well in that case then whoever wired it up before has overloaded the circuit and caused a dangerous situation

you should fit a economy 7 timer and connect the 2 immersions to that this means that there is a boost function using the top heater and the economy 7 uses the bottom heater but both can not be used at the same time

 

[glasgospark]

Well in that case then whoever wired it up before has overloaded the circuit and caused a dangerous situation

you should fit a economy 7 timer and connect the 2 immersions to that this means that there is a boost function using the top heater and the economy 7 uses the bottom heater but both can not be used at the same time

One supply ?

 

[Hawkmoon]

One supply ?

Yes they're designed for one supply (boost is by changeover switch)