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itsmoked, Thanks for the reply. Can you help me understand what you mean? Do you believe the curves (attached) that are published only suggest the mechanical life? Therefore any arcing will further reduce the life of the contact beyond what's stated on those curves? Why do they publish...

Hi I want to estimate the relay contact life that is switch some 120VAC solenoids. The manufacturer provides a graph listing expected operations VS switching current. That's quite easy to follow if you have one solenoid being switched by the contact. Question #1 But how do you determine...

In order to be in compliance with the CSA or Ontario Electrical Safety Authority (OESC) code, Can TEW machine wires or SEW appliance wires be installed in a conduit as interconnecting wires to provide 120VAC power from a transmitter to a remote sensor? I'm looking for 90+ Deg C rated wire to...

Hi I want to some feedback from others on this site. I have a touchscreen rated to -20C that's mounted outdoors but the response is often very slow and laggy during cold weather months. It often dips down to -10C around here. A slow touchscreen is a major annoyance for the users. I am...

One disadvantage I can think of is if the load at the end of this circuit suddenly drops and voltage drop is reduced then the transformer might be suddenly be over compensating creating a power surge. Are there auto tap changers in a transformer? Are they reliable? What about a voltage...

Is it good (and common) practice to use isolation transformer to boost the voltage? What is the limitation on boosting the voltage and are there any drawbacks to using isolation transformer?

Does this type of transformer exist? Primary and Secondary voltages are both the same, 600V, but it's Delta to Wye connected, 3-phase, ~400KVA. The reason for asking is, I want to take advantage of the taps in a transformer to give a small boost to voltage that is too low. Can this be...

I want to send set an alarm bit when the controller faults on minor or major watchdog error. I was thinking about using the GSV (Get system value) function to read the controller Fault Log. Should this logic be placed in it's own separate task and set as a periodic task type. If the main...

What is the reason that the code allows 125% primary o/c protection on a transformer and is it common/best practice to do so without secondary o/c protection?

The CEC code allows the use of overcurrent protection device rated at 125% of the rating of a dry type transformer with primary voltage below 750V, overcurrent protection on the secondary side is not required. Are the transformers built to withstand the load at 125% for long periods of time...

What is an acceptable level of voltage drop across the line and load side of a motor contactor? Is there an IEEE standard or manufacturer recommendation on this?

DPC, If it can carry 30KVA, would that be 30,000/120 = 250A on L1-N, L2-N, L3-N if they are all balanced 1-phase loads? To the transformer these are the equivalent of 250A / (120/208v) / 1.73 = 83A across L1-L2, L2-L3, L1-3?

How many amps of 120V single phase loads can a 3-phase 30KVA, 600V - 120/208V transformer delivery on L1, L2 & L3? What about 208V single phase loads? I understand that you can have 30,000/208/1.73 = 83A of 3-phase 208V balanced loads but I want to understand the single phase 120/208 scenario.

So in a ground fault sitution, you rely the electrical path created by the bonding wires which the fault current will travel on in order to return to the source (ie transformer). This low resistance short circuit (even lower in resistance than the path to earth ground) will cause enough current...

Why won't the overcurrent protection work? Wouldn't the magnitude of fault current be the same in either cases (with or without the bonding between the two earth grounds, see picture above) and the o/c will trip because of excessive current. Why would the magnitude of the fault current be...

So is the bonding wire between the two earth grounds to ensure the potential difference (if any) between the grounds is zero??? I am trying to the understand the need for this bond between the grounds when the grounds are installed properly.

By code and in common practice, is it necessary to have the same ground carried through from the source to the load? The scenario is this, a 15KV/600V solidly grounded transformer, 600V power is distributed and protected by breakers. One segment of a 600V circuit travels some distance on...

How do you proceed with the voltage drop calculation of a circuit that has various conductor sizes, material, lengths and 1 vs 2 conductors per phase? Do you start with the known supplied voltage and do the calculation for each section separately, use the calculated voltage result from the...

What's the proper way to terminate parallel conductors in a disconnect? The lugs would only except two wires that's one size smaller than the wires that exists. A distribution block in a separate junction box just before the disconnect?

Are fusible disconnects 100% rated for continous duty? Circuit breakers are often 80% rated, 15A breaker should only have 12A max of continous load. What about fuses, are there continous duty ratings on them?