what do you make of this???

[avinalarf]

Testing an installation today and have come across the following:

Radial circuit supplying outside SOs (via 4mm SWA) and ending up in Summerhouse at end of garden, providing SO and lighting within it. Circuit protected by 20A RCBO on TT system.

Summerhouse has been TTd (is that a word?).

Checking for R1 + R2 and got:

60.9ohms for SO on outside of summerhouse

187.9ohms for SO on other side of summerhouse wall

What could be causing such a large difference between SOs that are so close to each other?

 

[jl-heating]

whats a so`s ?

 

[Andy™]

possibly a corroded terminal. did you take from off or just plug tester in?

 

[Andy™]

whats a so`s ?

socket outlet

 

[sparkyt]

whats a so`s ?

socket outlets

 

[jl-heating]

lol ty.

 

[avinalarf]

possibly a corroded terminal. did you take from off or just plug tester in?

Initially I used the plug in tester, but undid the cover after getting that reading, but it was still the same.

Also...

Did IR test on RM and got the following:

L-N = 448ohm

L-E = 405ohms

N-E = 137.7ohms

I know they are all ok, but shouldn't the N-E reading be closer to the others???

 

[ianmacd]

Checking for R1 + R2 and got:60.9ohms for SO on outside of summerhouse

187.9ohms for SO on other side of summerhouse wall

Arnt these a bit on the high side? 100m of 2.5 is about an ohm or so isnt it?

Ian.

 

[Evans Electric]

Initially I used the plug in tester, but undid the cover after getting that reading, but it was still the same.Also...

Did IR test on RM and got the following:

L-N = 448ohm

L-E = 405ohms

N-E = 137.7ohms

I know they are all ok, but shouldn't the N-E reading be closer to the others???

What is RM Nat ? ?:| All the readings are high ?:| ? :| Did you do ins. test on Mohms scale ??

 

[avinalarf]

Hi EE

RM = ring main. Isn't it good for insulation resistance tests to be high??? Tester on Megohm scale.

It's the first time I've worked on a TT installation. Have been reading BRB for guidance.

 

[steptoe]

is this 3core SWA,?

sounds like they arent using the sheath for the earth and one of the conductors has broken down between the two SO on the summerhouse.

OR

one of the sockets is earthed via an exported earth and the other is via the rod at the shed.

have you got readings from the individual rods?

 

[ianmacd]

IDid IR test on RM and got the following:

L-N = 448ohm

L-E = 405ohms

N-E = 137.7ohms

I know they are all ok, but shouldn't the N-E reading be closer to the others???

Would have thought so, yes. I do not think I have seen less than >299M ohm even on old installations. Is this a new cable run?

 

[steptoe]

Hi EERM = ring main. Isn't it good for insulation resistance tests to be high??? Tester on Megohm scale.

It's the first time I've worked on a TT installation. Have been reading BRB for guidance.

be careful, some of that can be very misleading on TT systems,

remember when they used to say 21 ohm for a TT,

my how i wet myself........

 

[avinalarf]

Would have thought so, yes. I do not think I have seen less than >299M ohm even on old installations. Is this a new cable run?

No, cable run isn't new - probably original from early 70's.

 

[ianmacd]

Checking for R1 + R2 and got:60.9ohms for SO on outside of summerhouse

187.9ohms for SO on other side of summerhouse wall

Are these Zs or actually R1+R2?

 

[SPECIAL LOCATION]

Hi EERM = ring main. Isn't it good for insulation resistance tests to be high??? Tester on Megohm scale.

It's the first time I've worked on a TT installation. Have been reading BRB for guidance.

whether TT TNS TNCS

the final circuits.. R1+R2 INS RES etc...

would all be of "standard" type values appropriate to the lengths of cables used.

the TT bit only relates upon the external earth bit & Zs.

i.e.

TNS/TNCS Zs=Ze+(R1+R2)

TT Zs=Ra+(R1+R2)

so back to your cables???? :_|

Think you need to go back and check shorter sections of the cable,

may be a crap joint somewhere.

A wander lead may be helpful in this situation?

 

[avinalarf]

is this 3core SWA,?sounds like they arent using the sheath for the earth

3-core SWA was joined to circuit via a JB.

...and one of the conductors has broken down between the two SO on the summerhouse.

Is that possible over such a short distance? The only thing that separates these 2 sockets is the wood panels of the shed!

OR...one of the sockets is earthed via an exported earth and the other is via the rod at the shed.

Is this bad?

have you got readings from the individual rods?

I shall take a reading from the rod outside the shed - had only taken reading from rod for house Blushing.

 

[Evans Electric]

RM = ring main Ah ! I thought it was a 4mm radial SWA I'm confused now !! Also confused by not showing the Insulation test in Megohms . My own tester ( bit old now) often shows greater than 200 Mohm but no reading .

Were your readings in ohms or Megohms ? What about the Zs on each s/o ?

I' m that confused I'm going to bed !!

Deke

 

[avinalarf]

RM = ring main Ah ! I thought it was a 4mm radial SWA I'm confused now !! Also confused by not showing the Insulation test in Megohms . My own tester ( bit old now) often shows greater than 200 Mohm but no reading .

Sorry EE

Added my second query rather slyly within a response to an early post ]

 

[ianmacd]

Sorry EEAdded my second query rather slyly within a response to an early post ]

So if its a ring what are your values for r1, r2 & rn?