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Dear All, Is it required to have separate earth buses for "protection earth" and "instrument earth"? I know that the earth grid is the same for both. But as per IEEE 1050, we have two separate earth bus. As per IEC 61000-5-2 all earth busbars shall be connected to each other in each storey of a...

Thank you all Practical usage for this question is to calculate fault current in TT systems. (as well as better understanding the concepts behind any formula about resistivity of a rod to ground)

Thanks for all replies. I was asking about resistance between two rods (not resistance of combination of rods to the earth). In other words: resistance of each of these rods to the earth is 20 Ohms. What is resistance between first rod to the second rod? 40 Ohms? More? Less?

Hi everybody, Assume that there are two earth pits. Resistance of each of them is 20 Ohms (Calculated and measured). We connect an Ohmmeter to these two pits. Assuming negligible resistance for wires which connect Ohmmeter to pits, what will be measured value? Does it depend on distance...

Dear Dave, Our project is based on IEC. I usually add a lot of earth pits throughout the site. Then I make a ring around all buildings and tall structures by adding earth pits around them and connecting them together. Some earth pits shall be exactly below down conductors for lightning rods...

dear all, We have three types of earthing systems in our project: protection (power) earth, instrument (clean) earth, and lightning protection earth. Usually we provide separate earth pits for each type. Earth pits for PE are connected to eaxh other, but not connected to earth pits of clean...

Thank you. I dont understand last sentences. 909 replaces a generator by a voltage source (active component) and its impedance. So it behaves like 363. Why do you think 363 is more accurate?

Dear All, The IEC60909 is usually used for short circuit calculations in industrial premises. It is applicable for meshed and unmeshed networks; for 3 phase as well as unsymmetrical faults; for far or near to generator faults. It seems that we can use it everywhere. But there is another...

Here is motor datasheet, for further information.https://files.engineering.com/getfile.aspx?folder=9493df63-833d-4acf-964c-7c8a27c03477&file=IMG-20190129-WA0008.jpg

Thank you all for such great posts. One thing to add: six leads of the stator wires are accessible. So it is possible to verify wirings (star / delta). It is connected in star mode. If I connect it in delta mode, certainly the current will increase.

Dear waross. I believe that since FLA is 15A, then no load current should be about 5A. By measurements it is twice ! The motor is driving a small fan.

Thank you all. The motor and the plant are new. We are at the commissioning stage. Nameplate voltage is 380v. But supply voltage is 400v. Wiring is done in Y mode. As specified on the nameplate. The motor is not connected to vfd. I will check voltage for unbalanced conditions. But currents...

Hi everybody No-load & full-load currents of a new motor are too high. What can be the reason? Motor is: 7.5kW, 50Hz, 4 pole, full load current as per nameplate is 15A, but it is actually 24A. Measured no-load current is 10A. Motor is new. I have checked the terminal box and certainly the power...

Dear All, Many digital relays accept 0 to 1 A in their inputs for functions 50, 51, 37, etc. But what is maximum acceptable input value for a relay? As you know, current transformers saturate in case of short circuit. So they limit input current of relays. To select current transformer, we...

Dear All- What are normal values for Ith (thermal current) and Idyn (dynamic current) of protection relays?

Thank you for your information.

Thank you for your reply. We have 3 core cables both 400V and 6kV. Different voltage levels are laid in separate trenches.

Cables are laid touching each other

Dear All, Power cables installed beside each other, can not tolerate as much current as a single piece of cable. It is due to thermal effect of each cable on the others. IEC 60364 and IEC 60502 have specified correction factors for such arrangements. I am going to put two layers of cables...

We can connect the armour to ground by other means. Will it solve the problem?