At one of the job site we have, the service transformer at the utility pole is 3x 75KVA which gives 225kVA max capacity. Our contractor has previously procured a 1200A main service panel with a 1200A main circuit breaker, before he realized what the utility service will be. At 225KVA, the max...
When you have parallel generator (emergency standby, permament installation) in operations, through a set of parallel switchgear, is there any special consideration that requires the ATS to also switch the neutral? In the case of a single emergency generator, I always prefer to solidly bond the...
In the past when I did the short circuit study on the one line diagram and try to determine the AIC rating for devices, I was taught to make sure the AIC of the device can handle the fault current available at the point of my calculation. Lately, I wonder, as long as I know what the SCCR...
I just want to consult others on the following. In general for motor protection(typical 3-phase motor) using circuit breakers, reading the NEC, I got:
Branch ckt ground fault & overcurrent protection = not to exceed 250% FLA per Table 430.52
Disconnect device = min 115% - 125% FLA
Branch ckr...
Recently I was running into increasing the size in the electrical room and trying to account for all NEC clearances around the equipment, when a thought hit me. The equipment I was dealing are low voltage, from 208V to 480V as the highest. The thought was what about arc flash. I was merely...
Hi, has anyone heard of problems installaing premise distribution CAT 6 cables under (or within) floor slabs in open office environment? One of our customer has requested to install outside plant cables under the floor slab. His arguement anyting under the floor slab is considered exterior...
Does anyone know how to tell whether a currnet transformer is for zero sequence sensing and just a normal CT? For example, I am looking at the product page for one mfr. The product page did not mention anything related to zero sequence, so how do I know if it is for the particular application...
I am trying to understand the method to detect ground fault if you have an ungrounded system. In a few literatures I read that you will use relay 59G to sense gorunded overvoltage. Because the ground fault current in this setup is very small, they said that you will require a sensitive device...
Can you have ventilation openings for a NEMA 4X rated enclosure? Would that contratdict the definition of NEMA 4X, menaing splash-proof and protection against hose-down situation?
Hi, as I reading NEC Sec 430.103, regarding operation of the disconnect means for motor, I was puzzled why it stated disconnect mean must be rated for the locked rotor current, in case when the motor controller fails, which has its own overcurrent protection elements. If I only have a small...
I have triplex cable (3 cables intertwined together) with overlal diameter = 62mm. During pulling, because of the cable run of 350m, we decided to split it ionto 2 pulls from somewhere at midpoint. The trouble is, I failed to account for the manhole at midpoint, and when the cable is inserted...
If I have a cable that is 375m long, and wish to do a hi-pot test, I would imagine a DC test is more suitable because AC test would induce abnormal capacitive current across the insulation, and result in a larger leakage current. Does everyine agree with this logic? Also, is there a standard...
Just want to reassue my understanding of the requirement of bonding/grounding in manholes. My understanding is the requirement is only applicable if splicing of cables is done inside the manhole, and where the manhole is used only for pull-thru of the cable, there is no bonding requirement in...
I am not a structural engineer, but I wish to consult with others if what I have here is a problem.
What I am showing (attached) is a slab in grade pad with a concrete precast u-trench section on top, and the pad is about 347" x 120". The actually rebar dimensions are D16, at 150mm (or 6”)...
I have a question on HV able termination and want to consult others for their opinions. Being in Japan, we will have a switchgear equipment shipped from the US and where we have to terminate Japanese HV cable inside the cable entracne compartment. I am attaching a page from Schneider Elec...
Hi, this is question about sizing step-up transformer for a bunch of kitchen equipment loads that have various sizes compressors for refrigerators. These are small size compressors like 1/3 hp, 1/4hp, for ice machine, refrigerators, collers, etc. I have discussed the transformers issues under...
I am looking for a code reference concerning dry-type transformers that are being installed inside an enclosure outside the bldg. The situation here is we have a list of kitchen equipment where the user has ordered for the wrong voltages, as such we have to provide small individual step-up dry...
Just a question on twist-lock type plug and cord assembly, are they suitable for use as motor disconnect means, for motor size 0.4kW, used for transfer pumps? I am in Japan and the catalog cuts did not specifally say motor, or HP rating. When they say "device listed for motor disconnect" what...
I have a general question on efficiency on distribution transformers. In our specification, we specifiy 20000/25000kVA transformers to be factory tested to the standard of NEMA TP 1. In this case, according to the standard, which specifies the minimum efficiency levels for NEMA Class I liquid...
This is a question on 4 pole switching nuetral. In our specification we called for fusible manual transfer double throw switch rated for service equipment application, 225A, and a switching neutral. However, I have resreached several companies, they do not make any fusible switch that comes...
