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Thanks LowSpark. It is an existing manhole located outdoors. A "container" structure is being put in place 4'-0' above the manhole cover. So there will be access spaces around the manhole cover. I guess you can say access to the cover will be in a "void space" below the container structure...

Thanks!

Hello all. I have a manhole with 600v conductors. Looking for clearance requirements above the manhole cover. NEC does not state clearances. Could not find clearances in OSHA. I will be installing a structure over the manhole and will be limiting clearance above the manhole. Thanks.

So if I have a 3 pole, 100A, 480v molded case breaker, what is the procedure for testing? Do I need to remove the molded case enclosure to the breaker to perform a primary injection test and remove any shunt trips and then re-torque the breakers back into position? I have a manufacturer stating...

This is a follow up to the thread below: thread238-444329 Would you normally perform primary injection testing on single pole, 15A/20A molded case breakers rated at 120v or 277v? (what you would see in a typical 100A/225A commercial panelboard that serves plug loads or lighting)? If not, what...

Hi all. This is a general question - when a transformer feeds a motor, does the primary side also see a voltage dip during startup, in ratio with what the secondary experiences? We have a light flicker problem when a motor starts and one solution is to install a transformer ahead of the motor...

Per NEC 250.70, exothermic or mechanical lugs can be used to terminate grounding conductors to ground rod electrodes. Any benefit to either method? Thanks.

Is there a minimum size frame or trip rating to use primary injection testing on low voltage (<600v), molded case circuit breakers? NETA ATS does not define a minimum so one could assume it is across all frames and trips as small as 15A. Thanks. b

One driver manufacturer stated inrush was not cumulative. After doing further research I looked at NEMA 410 - Performance Testing for Lighting Controls and Switching Devices. They describe the testing procedures for testing inrush. It is cumulative and looks like from Table 2 that the...

This is for 480v, 60hZ three phase feeders within a building 200'-300' long. The feeders are lightly loaded.

We are running a low voltage (<600v) drop study in SKM and are coming up with a few values with a negative voltage drop. Curious as to why the results might be coming up with a negative % voltage drop result on some of the buses and feeders and the negative % results means. Thanks. b

Can anyone explain why driver inrush is not cumulative when having multiple drivers on a circuit. Is there a formula to determine the driver inrush when using multiple drivers? I have discussed the issue with several driver manufacturers and have not received a good explanation. Thanks.

Trying to determine how current changes when frequency in changed using a VFD. Voltage will change with frequency based on v/hz ratio. Hp change will be the cubed of frequency change. for simplicity, lets say HP = Volts x amps. If frequency changes 10%, voltage will change 10% and HP will be...

We have LED drivers with a rated inrush of 185 amps at 200 microseconds (.0002 seconds. We are trying to determine how many drivers we can place on a 20 amp, 120v circuit. The circuit breakers TCC curves start at .001 seconds. Also, the fuse TCC start at .01 seconds. What happens if the event is...

Hi there. We are trying to right size our electrical service. We asked the mechanical engineer if there was any "fluff" in their pump and motor sizing. They said yes. For example, the calculated BHP on one pump is 23 bhp. They selected a 30hp motor (a 23% increase). We ere thinking we could...

Thanks for the reading links Mike and redlinej.

Thanks for all the informative posts. Where can one read up on the topic?

Anyone know of a good book or article that discusses how the paralleling sources know, such as utility and distributed generation (pv, turbines, generators, and etc.)how much load generation to share? For example, with gas or steam turbine systems operating in parallel with the utility, how does...

There is no room indoors to install a transformer. The Owner doesn't want a transformer sitting around in his front or back yard. Unfortunately a step up and step down option isn't an option. In addition, if installed outdoors the transformer would need to be installed 4'-0" above grade to be...

Hi there. I have a 240v, 1200 amp single phase service for a residence. The length of run is about 1000 feet from the utility transformer to the home. The utility has stated they do not have taps on their transformer. Stepping the voltage up to 480v and then back down to 240v is not an option...