Fittings rated for continuous duty?

[vitoboy]

Hi all
So had some issues lately related to high current fittings .. dp switches mostly.
A number of electric boilers of various ratings .. from 7kw on up burning out their isolators .. the last one this week was a 7.5kw electric boiler running on a 6mm t&e cable 4m long from a 32A MCB .. 50A dp switch isolator.
No sign of cable overheating at the boiler (even though the terminal block is by the output pipe) . No sign of cable over heating at the consumer unit.. no tripping of the 32A mcb ..
So I understand the the cable is rated to carry over the 32.5 ish A which is max load .. mostly the boiler is modulating and no using anywhere near full power.
Now i know that there are issues with various 13A sockets that are not rated to supply 13A continuously 24 7 .. and these have caused problems with things like car charging.. we use all Hager fittings which I believe are all rated for continuous duty of there rated current... but many manufacturers sockets are not .. my question is are many dp switches and other fittings not rated for continuous duty at their started rating.. and this is causing them to fail at much lower loadings .. and if so how do I find out the continuous duty rating of such fittings.. I believe they should be published ..but a quick search tonight I can't turn up any ratings.
I know at the installation stage it's easy to over rate these things .. which I guess is why the installer for the 7.5kw boiler fitted a 50A dp switch .. but it still failed.

All thoughts greatfully accepted

Ta
Vito

 

[westward10]

Modern accessories are generally inadequate with high loads.

Glasgow 63A SP+N Fuse Switch Disconnector

Single pole switched neutral

www.cef.co.uk

 

[vitoboy]

Modern accessories are generally inadequate with high loads.

Glasgow 63A SP+N Fuse Switch Disconnector

Single pole switched neutral

www.cef.co.uk

 

[vitoboy]

Mmm.. but modern loads are getting bigger ..and more continuous.. and no one will win any jobs using fittings like this .. without being able to demonstrate a reason why .. such as continuous duty ratings .. but is there any such thing.?

 

[westward10]

The picture was a jest.

 

[vitoboy]

The picture was a jest.

But accurate never the less

 

[James]

As a general rule, I tend to over spec any equipment that will be run for long durations by at least 50%

 

[vitoboy]

As a general rule, I tend to over spec any equipment that will be run for long durations by at least 50%

Hi James ..
Yes I agree .. this was a 50A dp switch on a 32A circuit..
But any ideas where I can find rated duty info for manufacturers fittings so I can tell what to fit.?

 

[James]

An isolator should be rated for 100% duty.
however, over spec and it will last longer.

 

[westward10]

If the 50A switch was only suitable for intermittent use it would be stated as such.

 

[vitoboy]

If the 50A switch was only suitable for intermittent use it would be stated as such.

Thanks westward10 .. stated where?.. is that a fact or a suggestion?

 

[vitoboy]

I refer again to some manufacturers 13A socket outlets that are not rated for 13A continuous .. and some are .. such sockets intended for use charging cars for instance should be rated for 13A continuous.. .. does this apply to other fittings?

 

[davesparks]

Have you established what has caused the failure of the switches?

Do you have any clear pictures of the failed items, preferably with the cable still connected?

If the failure is due to the switch not being suitably rated then it will likely be the switch contacts themselves inside the unit which are failing.

If it is however not down to the switch itself but maybe a poor cable termination, which is far more common, then there will be a lot of obvious burning of the cable at the terminal.

What type of cable is fitted between the isolator and the boiler?

How many installations has this happened on?
Has it been multiple times at the same installation?
Were they all connected by the same contractor?
Could they or a supllier have bought a job lot of isolators which just happened to be from a faulty batch?

Have any of the failed isolators been returned to Hager for investigation?

 

[vitoboy]

Hi Davesparks
The installations are varied and not linked by type or installer.. but by loads such as electric boilers ..Hi current continuous loads .. that seem to be installed correctly..
The most recent that I'm referring to as an example was actually a schneider electric 50A dp switch that had failed ..it was welded in the on position both live & neutral supply and load side cables overheated for about 25mm from the terminal.. terminals seemed good and tight but its hard to be sure at this point.
No cable thermal damage at the boiler end or the consumer unit end ..no tripping of the 32A mcb .

I was using hager as an example due to the stated duty rating of there 13A sockets being for continuous load 24-7 .. and wondering if this applys to other fittings like dp switches and isolators.

But we have seen the issue with various brands of dp switches.. we all expect cheap ones to fail .. but they all seem suspect..pretty much always on a circuit rated less than the switch that has failed.. 40 / 50A dp switches on 32A /40A circuits.

So again I want to know is there a duty rating and if so where can I find it so I can spec appropriately.

 

[davesparks]

So again I want to know is there a duty rating and if so where can I find it so I can spec appropriately.

Unfortunately I don't know the answer to that, I've never tried to use that type of isolator for a true high current load.

I would be considering a good quality rotary isolator if it is going to be located somewhere where an ugly ioskator isn't going to be a problem. And as far as good quality rotary isolators go I'd use Craig and Derricot.

 

[LewisM]

You can contact the Hager support on WhatsApp and ask they normally reply within a day

 

[RichardM]

You mentioned the isolator failed but then referred to it as a switch. An isolator is not designed as a switch, I know it does the same kind of job but it is not designed for continuous on/off usage. An isolator is used to isolate an item of equipment from the supply (for maintenance, long period outage etc. ). They will (eventually) fail if used to disconnect/connect an item under load due to arcing.

 

[Lucien Nunes]

There is a difference between duty cycle and ultimate endurance. A device with limited duty cycle will overheat the first time it is exceeded. E.g. a tool transformer with an intermittent rating will, if loaded to that rating, keep on getting hotter until it is significantly overheated and possibly damaged.

Most pieces of switchgear should be able to withstand their rated load continuously. I.e, if a 20A switch is loaded to 20A it will not continue getting hotter to the point that it overheats. The problem instead is endurance, for which the testing requirements in the BS are probably not sufficient to ensure all products offer the kind of endurance we would like to expect. For example, a BS1363 13A socket outlet must be tested with 14A load on one (to stress it) and 6A on the other (to balance the total to a representative figure). It must stabilise at a certain temperature rise that will not compromise its operation or safety for the duration of the test. But, crucially, it does not say that the socket must be able to do this at ten years old, or even one year old.

That means it's down to the manufacturers and different products might have different test regimes applied. To be sure of what a product can be expected to withstand, I would consult the manufacturers and make no assumptions. For example, I suspect that occasional opening and closing of the switch or isolator will dislodge accumulated oxide and sulphide from parts of the contact surfaces that are not in gas-tight contact, that eventually grows and starts to relieve some of the applied force from the current-carrying asperities. So an endurance test that specifies switching off and on once every six months might not represent the conditions where that never ever happens, trivial though the difference might seem.

 

[vitoboy]

You mentioned the isolator failed but then referred to it as a switch. An isolator is not designed as a switch, I know it does the same kind of job but it is not designed for continuous on/off usage. An isolator is used to isolate an item of equipment from the supply (for maintenance, long period outage etc. ). They will (eventually) fail if used to disconnect/connect an item under load due to arcing.

Hi Richard
Yes .. this had not been used to disconnect at all as far as we can tell .. never been used since installation in fact.
We have always advised customers not to use there shower isolator to switch the shower on and off on load for this reason.
I refer to the isolator as a switch because I'm typing a lot and lazy.!.

 

[RichardM]

Hi Richard
Yes .. this had not been used to disconnect at all as far as we can tell .. never been used since installation in fact.
We have always advised customers not to use there shower isolator to switch the shower on and off on load for this reason.
I refer to the isolator as a switch because I'm typing a lot and lazy.!.

One thing I didn't mention and that is decreasing quality. I have wired many switches over the years, decades, feels like bloody eons and the quality of fittings has definitely gone down hill, just about everything appears to be made in China?
I am also a fan of Hager but not for their shower isolators. I prefer the Crabtree, they are easier to fit giving a little more room to maneuver 10mm cable into position. They also have a deeper feed in for the cable & if I remember correctly 2 securing screws per 'pin'. I would always prefer to fit a wall mounted isolator but few customers will (understandably) wear the additional cost of chasing, plastering etc.