110 volt 16 amp sockets on a 32 amp ring

[Flanders]

When caring out an EICR on a site I found that the 110 volt socket outlets were connected as three 2.5mm ring final circuits each protected by a 32 amp MCB (single Pole) in a DB fed from 110 volt transformer ,These sockets are used to supply halogen Flood lights that area plugged in when required ,there is about 10 on each circuits

Now I know this is not the correct way of doing it ,as I would of installed radial circuits protected via 16 amp double pole MCBs

There for due to the possible over load of the 16 amp sockets and the fact that there is no over current protection on the return leg I gave this observation a code 2

Am I being over the top as this installation has been in use for a least 10 years and is showing no signs of thermal effects

As thinking about it ,the lights that are being used will not overload the sockets and the 2.5mm ring can not be overloaded as the 32amp mcb would trip out ,

Only problem is any other appliance could be plugged into the 110 volts sockets so this was also my thinking for the code 2 observation

 

[Lucien Nunes]

A lamp is unlikely to cause an overload as it will tend to blow very quickly if much of the filament is shorted out, so in one sense it's a fixed load. But certain types of lamp, especially small powerful halogens, can flash over inside the bulb as the filament breaks and draws an arc. To control the damage the lamp maker will specify a maximum fuse or MCB rating and curve, to limit the let-through in the event of violent lamp failure.

I have been standing next to a Par 64 that had a lamp flashover when protected only by a B32 and it was like a cannon being fired - A singing arc for about 1/2 second followed by a huge flash and bang and broken glass and quartz shot out of the front all over the room. A linear is unlikely to do this because the terminals are so far apart but still I would respect the manufacturers' fuse specs.

 

[UKMeterman]

Hi,
I have seen linears explode as well, very nasty as they were being used for indoor down lighters in a church. There was no intervening glass shield. When they fail the arc causes the pressure pulse causes the quartz tube to burst.

In this particular case it may be the impedance of the 230-110 transformer that has limited the fault current of any arcs that they have had. I would also suggest getting the MFT out and check the prospective fault current is acceptable for a 32A circuit breaker.

 

[Flanders]

The only test of done so far is ring continuify on the live 1.74 , neutral return 1.77 and earth 1.70 , IR of 128 live to live and 127 live to earth , i have not done any live test yet not sure if my mft will test at 110 volts i will have to check , i am going back to the site in a couple of weeks so will do some more investigation then. As these reading are high i think this is another reason to down rate the mcb to 16 amp