Storage heater insulation resistance

[Res is futile]

Hi. everybody. This is my first post on the forum . I have recently replaced a consumer unit for night storage heaters and have used a dual rcd board to comply with buried cables requirement. Rcd would accasionally trip during the night. I have isolated the fault to one heater. I have powered this from the day rate supply, and measured the insulation resistance to earth when cold and then again after half an hour of heating. The insulation goes from greater then 999 M ohms down to 17 M.ohms and as the heater cools it goes up again. I did not have the time to leave it and see if it tripped the day rate rcd. I am confused as in my limited exp with storage heaters, the resistance increases as they heat up and dry out. Have I got a faulty element or could it be another component, and if so is it worth trying replacing the elements ? Thankyou for any advice.

 

[nickblake]

Firstly my friend when people say storage heaters it rings alarm bells for this reason ASBESTOS , before you work on storage heaters you should check the age as they may well contain asbestos ,any thing pre 1986 .now to the problem , the tripping rcd could be due to the element in the storage heater breaking down , another thing could be earth leakage due to all the storage heaters switching on at the same time , if you get hold of an earth leakage tester and test the suspect heater circuit for earth leakage , think youll find the elements are faulty , these can be replaced but as ive mentioned beware of asbestos

 

[Res is futile]

Thanks Nickblake. I thought of earth leakage and put the suspect heater on one rcd on its own and put the others on the other rcd. They all came on ok but the faulty one tripped the rcd on its own. Am I right in thinking that the faulty element's insulation is breaking down as it heats up and eventually gets low enough for a small earth leakage to upset the rcd? I will certainly be careful of asbestos but don,t think the heater is that old. Cheers.

 

[nickblake]

it does sound like it . what you need to do is first dush sheet the floor as their will be alot of dust and its often black and will stain the carpet , remove the front panel and remove the front row of bricks this will expose the elements , depending on the storage heater size it may have 1 2 or 3 elements , check the elements for splits or cracks you may well find an element in bits as the other element will work as they are wired in parallell , take an element out and get a replacement , i would recomend you replace all the elements

 

[Res is futile]

Thanks Nick. Would any 850 W element with the same terminals work ok or do I need to get storad ones as they are more expensive and the heater belongs to a pensioner. Thanks again for your help.

 

[nickblake]

Always better to install the correct element , shop around and get the best price