A service point is located inside the utility substation. The customer owns and installs the conductor to the service point. The service conductors are underground in conduit. Does 250.186 require a wire type supply-side bonding jumper from the service point to the service disconnect? 250.190...
Located in central US where we own some wind farms and have power purchase agreements with many dozens of others. It seems that at all of these locations, the transformer at the collector sub (35kV to transmission) is a GndWye-Delta-GndWye configuration. I have a few ideas of why this...
I don't know much about three winding transformers and I need some help figuring out what impedance value I should use. A look at our data base says that the impedance of the transformer is 11.28% (I'd expect two values, one for each low side winding, but there is not). Below is a snip from the...
March/April 2019 Industry Applications Magazine
"A History of Grounding and Earthing Practices in the United States Part 2"
If you've read this article, what do you think? Do you agree with the conclusions?
I am looking for general advice, rules of thumb, or best practices but I also have a specific project I am looking for guidance on.
Overview of my project: I need to install instrumentation and control cable from an existing DCS cabinet to a new junction box. Cable distance will end up being...
I have been brought into a project to install an already purchased and delivered air compressor from a well known maker of air compressors and I am struggling with two issues:
(1) The SCCR value given on the nameplate within the electrical enclosure compartment in the compressor package is too...
When reading about series ratings I often see mention of fuse-fuse, breaker-breaker, and fuse-breaker series ratings. Two questions about this:
1.) This first question is in regards to the NEC specifically:
Since series ratings are mentioned under part VII. of Article 240 and not under sections...
Using the NEC (2014) definition of service point.
Can the service point be located inside of the service entrance equipment?
Said another way:
Is there any situation in which the conductors entering service entrance equipment can be either a service drop or service lateral?
Or said another...
Recently jumped the fence and started working at a utility. I am still trying to get up to speed on rules and requirements for utilities. I am working on some projects where they are using a fuse and circuit breaker in series: the circuit breaker has too low of an interrupting rating for the...
First, am I correct in believing that (3 pole) low voltage circuit breakers have both a 3 pole and single pole interrupting rating? If so...
Generally, are the interrupting ratings provided in technical literature for MCCBs, ICCBs, and LVPCBs and the like a 3 pole interrupting rating, and is...
For those who have a copy of IEEE 142 2007:
Section 1.9 is "system grounding for uninterruptible power systems"
I believe the descriptions provided in sections 1.9.2, 1.9.3, and 1.9.4 don't match the figures referenced (Figure 1-38, Figure 1-39, and Figure 1-40).
I agree with the...
Working on a project where the local utility will supply the transformer for a new facility (13.2kV wye/480V wye, 750kVA). Incoming voltage is 12.47kV. We will be using a high resistance ground on the 480V side to limit SLG faults to 10A. Positive and zero sequence impedances of the utility...
I'm curious if the following hypothetical installation would violate article 225.30 of the NEC.:
1000kVA 480V transformer outside of building feeds two 600A MCCs inside of building. Each MCC has a main breaker.
Since the total load is less than 2000A I don't think it meets the requirements of...
I am trying to chose correct cable sizes for a new underground electrical duct bank. I am using the 2011 NEC to determine the correct conductor ampacities. Since this is for 480V, I think could get away with using Table 310.15(B)(16) and be done with it, but I am not comfortable with this...
IEEE 141 mentions a few classifications for transformers and I'm trying to understand the differences.
The first classifications mentioned are distribution (3-500kVA) and power (>500kVA). The next classifications mentioned are substation and unit substation. It says the difference between...
I was out visiting one of my company's plants recently and found some MCCs that are main lug only. The protective device for each MCC is a low voltage power circuit breaker in a nearby switchgear. I know switchgear is built to have a 30 cycle withstand rating, and the LVPCBs can be selected...
I have no interest in implementing series rated systems but I'm wanting to know some more information about it.
1.) How can you obtain a series rating per NEC 240.86(B)? I understand that the OCPDs must have been tested together by a NRTL - the meaning of this isn't entirely clear though. Can I...
I asked ETAP support this question already, but they informed me that my employer has allowed the support agreement to expire and thus won't help me. So, I thought I would ask here before spending $2k on the support for 6 months.
I am trying to do a coordination study in ETAP. There is an...
I've seen it stated in several places that special consideration needs to be made for corner grounded delta, high resistance grounded, and non-grounded systems regarding the single pole interrupting rating of MCCBs. I understand why this consideration must be made, however I don't understand how...
I was recently at one of my company's plants looking at their MCCs because they wanted me to determine if they have capacity for an expansion. While I was looking at the MCCs I noticed the nameplate say the MCCs have a 10kAscr. The refinery that the plant is attached to includes the plant in...
