testing mcc boiler house control panel .

[hughesy124]

testing a mcc panel to day took ze at panel got 0.16 .then went to first mcb a 6amp c rated .zs was 10.56 which is very hi. did all checks to see if it was a bad earth . all looked to be ok .did r1/r2 reading which are ok .would hi zs reading be from mcc control gear .how can i get the right reading for test sheets.all help welcome many thanks .ps this is my first time on this site.

 

[londonlec]

Was there an RCD and did you test using no trip function?

What was your R1 and R2 result?

 

[hughesy124]

no rcd all mcb type c motor rated .can't mind r1/r2 reading but were low can check reading tomorrow.

 

[cstewart37]

If the circuit was a motor through a DOL starter this is quite possible, especially if the overload is of a low range. We have stopped fitting overloads under 1 amp. Remember on a single phase over load the live goes through the overload twice and the neutral also goes through the overload and there is also quite a high resistance through the mcb. This is why HRC fuses are common in MCC panels.

 

[hughesy124]

i think it has something to with the mcc control gear not sure what to do as boss needs all test sheet asap.

 

[hughesy124]

testing a mcc panel to day took ze at panel got 0.16 .then went to first mcb a 6amp c rated .zs was 10.56 which is very hi. did all checks to see if it was a bad earth . all looked to be ok .did r1/r2 reading which are ok .would hi zs reading be from mcc control gear .how can i get the right reading for test sheets.all help welcome many thanks .ps this is my first time on this site.

need help

 

[Knobhead]

When you say a MCC panel, are we talking of 2 or 3 drive or dozens. I ask because it would change how I would earth a panel. The 2[SUP]nd[/SUP] question is where are you taking your readings from?

 

[hughesy124]

hi it;s a boiler house control panel .The reading is coming from top of dhw pump isolator with the switch off . looking to get Zs reading to fill in test sheet . looks to be a Trent system .also switch all other off to see if that would help but still the same very hi about 10.56 ohms ..check all other in boiler house and all are coming back the same.

 

[Blowcat]

If you got time and really wanna find the root cause of this high Zs I would take a Zs at the mcc panel where the outgoing circuit leaves and connect your testers earth to the outgoing conduit/trunking/swa so your testing the outgoing circuits earth path and not direct to the panels earth bar.
Go to each point and get a Zs untill you find the cause. remember to test the in and out side of switches.
An R2 test would let you know if your cpc condition so if that was low the high Zs may be due to control equipment or a fault switch. Is the trunking earthed? is there a seperate cpc of is it main frame, and corrosion?

 

[hughesy124]

back on job at the end of the week will give it a shot.many thanks .

 

[i=p/u]

Why not just add r1 + r2 too ze and

 

[Farmelectrics]

put the 10.56 value in an explain to your boss it requires further investigation gets your boss of your back let us no the outcome

 

[cliffed]

Had exactly the same results when testing at isolators,supplies going thru o/l of contactors, all other tests R1 + R2 were fine.Reported to gaffe,still dont know the outcome ta ra bab

 

[hughesy124]

put the 10.56 value in an explain to your boss it requires further investigation gets your boss of your back let us no the outcome

He said he put note in test sheet about hi reading .that his answer.

 

[hughesy124]

If you find out any more let us know many thanks.