RCD Tripping times question

[Moortown89]

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A few 30mA RCBO's that i have tested recently are tripping lower at x1 than they are at x5, e.g 13.1 x1 13.8 x5, I know both these results comply but im curious does any one know why the 1 times trip is lower than 5?

 

[Electro-tech]

Are they AC or Type A RCBOs ? Are you testing at the Distribution panel?

 

[Moortown89]

Are they AC or Type A RCBOs ? Are you testing at the Distribution panel?

Type A RCBO, Yes being tested at the DB

 

[newfutile]

This is within error of measurement or maybe the inductance adds a tiny bit that is usually cancelled out by the increased current . In any case we don’t test at 5 x any more.

 

[Moortown89]

This is within error of measurement or maybe the inductance adds a tiny bit that is usually cancelled out by the increased current . In any case we don’t test at 5 x any more.

Sorry should have stated it was for job done in the south of ireland were they still record times 1 and 5 on the test sheet

 

[newfutile]

I take it they don’t use BS7671 there ?
in any case i would guess coil rise time is providing a slight delay which is not offset by the extra current flow , its only a guess though only the manufacturer would really know why, are you testing just the device as a type AC with all loads disconnected? , possible load capacitance or inductance might play a part.

 

[Risteard]

This is within error of measurement or maybe the inductance adds a tiny bit that is usually cancelled out by the increased current . In any case we don’t test at 5 x any more.

Just to be pedantic I would suggest that we don't record the 5* test anymore, but aren't precluded from carrying it out. Although if it doesn't disconnect within 40mS @ 5 I delta n this may not necessarily be a failure.

 

[newfutile]

GN3 says that too many test will shorten the life span of the device and to counter that a 5 times test is discouraged,however I’m not sure I believe that ,most rcds I come across suffer from stiction .

 

[pc1966]

I can't accept the "reduces life" argument either. I'm not sure what the official standards say, but the Hager catalogue mentions "Mechanical life: 20,000 operations" for one of their RCBOs. Sure it will be slightly less on-load, but when testing RCD trip times that is usually on no (or very little) load.

If you assumed el-crapo brand has a life of 1000 operations, and your full test has 5 trips (one on test button, then four covering In and 5*In on 0/180 deg) that is 200 tests. How many times per year do you check things again?

As @newfutile says, I am more worried about devices sticking because they never get cycled!

 

[newfutile]

We have a rcd test socket for our monthly calibrations ,we have 2 electricians doing at least 4 trips each per month for the last 5 years , it still trips at 19.6 ms every time.
that’s still only 480 operations.
if we assume 1 test button test every 6 months ,plus 4 every 5 years (in out tenanted properties here) 14 operations every 5 years don’t seem that excessive to me.