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Please send me some links, documentation with MV measurement . I am kind of confused when i see 2 ct-s, 3 ct-s, with 2 secondaries, 3 secondaries. Or 2 VT-s, 3 VT-s , in star, delta, etc... Thx.

Well, relay coils in parallel, or voltage monitoring after fuse does not indicate if fuse have melted. It indicates voltage absence, as well. I found some solutions at Siba, Bussman- simple switches, and Jean Mueller- electronic relay...

Thanks for reply. There are 2 models needed: 1: for 3 HRC fuses 40-100 A. Fuse monitor has 1 NO+1 NC contact, used in control. 400 V AC. 2. for 220 VDC fuse, 6 A, to protect control voltage in LV switchboard drawers. Fuse must be small, for example bottle type.

Hi Can you give me some technical description of fuse supervision -(some relay or other method to monitorize fuse melting)? Also some models and manufacturers? Thanks.

Waross, you said: "The neutral must be free of intentional grounds between the neutral CT and the load. " No. Those groundings are all intentional. Those grounds are the problem, and the normal current(not fault current) will have the shown path in my drawing, i believe! So, the earth fault...

I add a little sketch.http://files.engineering.com/getfile.aspx?folder=ee7afee8-af53-4e9c-986b-e15dcc14fe82&file=Multiple_Earthed_Neutral_UEF.pdf

Hi . For a multiple earthed network(the neutral wire is earthed at the powerhouse, at the point of supply to each consumer and at other points along the line between powerhouse and consumer), I have to use 3 p ACB, that's clear. But designer wants Ground fault. And CT on neutral. I know ground...

I do not think there is a Standard that shows as mandatory using 5 wire cables(or 3 wire in case of 1phase loads). You can use 3p+N cables, and connect PE from grounding system of building, with steel band.

No, IEC standards govern, and local codes from Romania.

Do you know the standard value of illuminance inside an auto repair workhouse? And which IEC standard shows illuminance values? Thx.

Hi Does anyone know what is the short time withstand current of the bars fed by 2, 3, or 4 transformers, let's say 630 KVA Uk=6%? If the Icw(1 sec)= 15 KA for bars fed by 1 transformer, for 2 transformers Icw(1 sec)= 2x15KA , for 3 transformers is 3x 15=45 KA? Is this the rule? Thanks.

Back to topic: So: There is no method to find which one is A? Just to trace the phases all way back to generator. And more: it doesn't matter which one is A. If u have to connect 2 circuits, just to be sure that there is no phase difference between them. I have found something, but it is too...

Great. I measure all 3 voltages. And i will have voltage information. But how do you measure which is A?

Hi I am disputing with a colleague: I say : Phase "A" exists. every 3-phase system has a phase "A" He says: Phase "A" is random. Important is just the rotation ABC, or BAC. You cant determine which is A. I believe: every circuit has a phase A, that can be measured, and labeled as A. If there...

Slava, 86 relay sends "Open" command? I thought it sends "NO close until reset" command? Regards

I am back with this: One 86 relay can be used for more than one circuit? Let's asume 5 circuits. I mean, if 1 trip is detected, all output contacts will open, and circuits of all 5 closing coils of circuit breakers will be open? This will not be a problem, i guess. Thanks.

Hi If we have 3x capacitor banls 300 KVAR in a LV switchgear, we got 3 power factor regulators. How do this Power factor regulators take the informations about currents- i need 1 CT on main bus bar/each regulator ? Or (maybe)if i have on main incomer 1 converter 5A - 4-20 mA, can this be...

Really great answer. Thanks jghrist.

Maybe my english was bad... I mean the bolts are connecting the joints(in fish plates, at connections between horizontal busbars ). Those bolts are not insulated, and the rest of bar is. Need to insulate also bolts(against accidental touch, etc).

Hi Does anyone know a good material to insulate the bolts from the bar joints in a 400V switchboard? Thanks!