Help to solve mystery electrical outages,

[paulroberts]

We have been called in to assist diagnose irregular power outages to a restaurant in th uk.

The restaurant is fed via a 3phase and pme combined neutral and earth.

At irregular interval power drops at either the Kitchen DB, which is tpn fed via swa via switch fuse from a bus bar chamber or the Front of house db, which is tpn fed via swa via switch fuse from a bus bar.

the outages last from a second to 10 minutes, and affect all circuits connected to the relevant db.

The problem we need help with , is that data loggers prove that during each outage ( they do not affect both boards at the same time)

Voltage and current is lost to the affected board, however not loss of voltage is recorded at the bus bar chamber!

The sub mains cabling and gear is all new, and there are no inline switching devices between the switch fuse at the bus bar chamber and the incoming isolator at the db.

These faults have been present for 6 months, during which time, a complete new distribution system has been installed, 80% of the premises rewired. And the whole installation tested.

The electricity board have carried out logging and ZE and ZS to prove supply.

The shortest outage recorded was for less than a milli second, which would eliminate most switching devices.

Has any one ever come across any thing similar?

 

[Phoenix]

Is this the same issue that was posted about on iee forums about a month or so ago?

 

[steptoe]

have the submains been verified?

maybe there is a ghost.........

 

[Evans Electric]

Does this occur at times of high current use , ie; When cooking at busy period .

 

[sparkytim]

A similar issue turned out to be an unhappy employee flicking main switches, discovered eventually after much effort by CCTV evidence.

 

[Steve3948]

Have all Bus-bar clamps been checked, had a commercial cooker doing this and found the clamps hand tight to switch fuse.

 

[paulroberts]

Is this the same issue that was posted about on iee forums about a month or so ago?

It may have been, problem has been there since October last year,can you forward me a link to the iee forum please?

---------- Post Auto-Merged at 09:17 ---------- Previous post was made at 09:11 ----------

All sub mains are new and verified.

Bus bar clamps have all been torque tested.

We don't believe it can be an employee as they would have to turn the switch fuse on and off in less than a second, engineers have been sat in switch room during outages.

Outages only occur when the kitchen is running,but may be only once a day?

 

[kerching]

Bearing in mind that I know nothing [see wife for details]

I would go for a dodgy busbar connection assuming you have proved everything up to the and including the busbars

A torque test does not mean it is right...turn it off and give them a tug [turning OFF being the main tennet of this action]

Thermal imaging camera

If it is all going Melinda Messenger I would suspect a dodgy neutral

Megger [Ok then, Insulation Resistance Test at an elevated voltage in line with BS7671 as ammended] the 4r$e out of it NOT just by giving it a quick 'button press'....meg it for a few minutes

...............there again, what do I know................................ :coat

 

[Andy™]

do all 3 phases go off or just one of them?

if tis all 3, then its got to be something that controls all 3 phases, like a faulty MCB?

 

[Evans Electric]

It all smacks of loose connections to me. All tightened to the correct torque eh ! Blimey thats a first in my experience.

Where does one find the correct torque for bolting a lugged cable to a busbar ?

 

[batty]

So it is only going off under load which means its a connection problem somewhere. No loss at busbar so its not a DNO problem. So the options are a connection in a switch or a connection at the busbar. Has quality switchgear been used. I have just used an economy switchfuse which is rated at 80 amps this was a rotary one. I much prefer the mem type with a handle but customer opted for the cheaper option. Not sure if it will stand the test of time. Other thing it could be a faulty main switch in the distribution board. As others have said torqeing busbar connections seems a bit strange I personally do them up until they are tight. Is it quality switchgear that has been used?

 

[Manator]

It all smacks of loose connections to me. All tightened to the correct torque eh ! Blimey thats a first in my experience. Where does one find the correct torque for bolting a lugged cable to a busbar ?

5/8-11 lug bolts should be torqued to between 55 and 70 foot-pounds. 1/2-13 lug bolts should be torqued between a range of 35 and 50 foot-pounds. 3/9-16 lugs require a torque of between 20 and 30 foot-pounds. Lug bolts sized 1/4-20 should be tensioned to within 5 and 7 foot-pounds.

M6 bolts should be torqued to 7.2 Newtons per meter. M8 bolts should be torqued to 17 Newtons per meter. M10 bolts must receive 28 Newtons per meter of torque. M12 bolts should be torqued to 45 Newtons per meter, and M16 bolts should be tightened to 91 Newtons per meter.

Do you mean something like this?

 

[kerching]

Said slightly tongue in cheek, quote 3/9-16 lugs require a torque of between 20 and 30 foot-pounds. where did that one come from OR have you had as much Merlot as I intend to have F Shortly?!?!?

Seriously though, I am the proud owner of a VDE 1000V socket set, torque wrench and a host of other frightening stuff. I mainly use Herman Goering 1600A panelboards , and I always torque the crimped lugs up to what the manufacturers advise in the gubbins that comes with the board. For the stuff that I do I feel it would be frowned upon, and somebody would go all sulky on me, if the connections were loose and the server room /farm/whatever went down! As to why all this stuff is 1000V................because my Family is worth it!

 

[Manator]

Typing from a list without the help of a proof reader kerching, I am not editing again though

OK I have edited. :innocent

 

[paulroberts]

Typing from a list without the help of a proof reader kerching, I am not editing again though OK I have edited. :innocent

The switch gear is all brand new Snieder.

All connections have been tested,checked, pulled pushed.

We have ruled out loose connections and dodgy switch gear on the basis that the outages are affecting 2 separate sub mains albeit connected to the same bus bar.

A loose connection would generally have other signs such as elevated current at times of higher impedance, or signs of over heating.

The load has been diliberatly unbalanced to create stress on the neutral to try and recreate the fault ( as we assumed a neutral issue due to the commonality of the issues) this changed nothing.

The outages appear to move from one board to the other???

We have ruled out sabotage as the pub chain moved out all the staff for two weeks and brought in new, and the issues still appear?

The voltage and current are lost across all phases and neutral at time of each outage.

 

[steptoe]

mmmmmm

isnt 1/2" closer to 12mm ?

BTW, the torques you have given, are they the fallbacks? I would assume so as otherwise different manufacturers wouldnt state different torques for different situations or thread material........

not trying to be pedantic you understand, just so some people dont mistake those figures for every bolt in every situation.

 

[Manator]

The torques I have given are for electrical lug connections to bussbars. The idea is that the lug itself will heat up greater than that of the copper conductor if the connection is loose. Most torques are given for the size of the lug bolt and not the lug, not forgetting that all lugs would have to be sized for the bolt anyway.

However as you correctly say if there are any manufacturers instructions these should always be followed.

 

[kerching]

5/8-11 lug bolts should be torqued to between 55 and 70 foot-pounds. 1/2-13 lug bolts should be torqued between a range of 35 and 50 foot-pounds. 3/9-16 lugs require a torque of between 20 and 30 foot-pounds. Lug bolts sized 1/4-20 should be tensioned to within 5 and 7 foot-pounds.M6 bolts should be torqued to 7.2 Newtons per meter. M8 bolts should be torqued to 17 Newtons per meter. M10 bolts must receive 28 Newtons per meter of torque. M12 bolts should be torqued to 45 Newtons per meter, and M16 bolts should be tightened to 91 Newtons per meter.

Do you mean something like this?

ermmm..............I think you will find that you havn't............. :innocent

---------- Post Auto-Merged at 15:35 ---------- Previous post was made at 15:28 ----------

mind you I am sat in the garden with Queen Live at Wembley playing at full blast on the Garden speakers, to drown out the incessant whining and inane drivel falling from the mouth of the cretinous biatcchh next door along with the barking of her fricking dogs [5 boxers at last count...Patch, can I do anything about this????? they bark and my Jack Russells come inside FFS]

Mr Merlot is assisting me with my VAT Return...so much easier with him helping. Oh S4ite she is lighting barbecue now, must go and lend her some petrol....... :Y NUN F E C K A R $ E.............. :coat

 

[Steve3948]

What type of switch supplies the bus-bar, it could be whichever sub-main pulls a sudden load affects faulty contacts on said switch.

 

[philbas]

The switch gear is all brand new Snieder.All connections have been tested,checked, pulled pushed.

We have ruled out loose connections and dodgy switch gear on the basis that the outages are affecting 2 separate sub mains albeit connected to the same bus bar.

A loose connection would generally have other signs such as elevated current at times of higher impedance, or signs of over heating.

The load has been diliberatly unbalanced to create stress on the neutral to try and recreate the fault ( as we assumed a neutral issue due to the commonality of the issues) this changed nothing.

The outages appear to move from one board to the other???

We have ruled out sabotage as the pub chain moved out all the staff for two weeks and brought in new, and the issues still appear?

The voltage and current are lost across all phases and neutral at time of each outage.

I'm not an expert but iI would be haveing a good look at the one thing they both have in commen