Let’s close January with a bang. Join me at 12:00PM Eastern on January 31, 2025. Just click and book mark it. We still have questions coming in and as usual we’ll field on the fly during the call.
Here is where we tackle questions that have been made to some of my videos and that have come across my desk related to technical topics. We will continue our discussion on selective coordination which is a topic that just won’t go away and take on a few more. I”ll keep this as a running list moving forward.
Questions on the table
Maybe this has been said, but I think that boat hoists are different from Boat Lifts. So both terms should be included, and defined. I think I boat hoist is one of those thing where you put your boat in the slip and then lift it (hoist it) out of the water for whenever it is not in use. The LIFT brings the the boat up and out to be stored elsewhere.
Good morning Tom! I’m sending you this text because I know you’re busy, but I have a question about GFCI . . . what are the load side conductor length limits for class A GFCI protection, in other words, at how far away do you either lose effective GFCI protection or begin to have nuisance tripping due to capacitive or other effects?
This question’s comments on the thread with the group moderator and group expert only generated more questions: the expert and the moderator both said a 240V GFCI can run farther than a single pole with neutral. Is this true, and why? The moderator claimed that the 240V GFCI can be farther away because small leakages get offset line to line, “L1 leakage to ground (EGC) gets cancelled by equivalent L2 leakage to ground”, because the L1 leakage current flows in the opposite direction than the L2 leakage current and that the electrons flowing are returned alternatively to and from the ground so that none flows back to the system on the ground. I said that the ground is effectively in parallel, and that flow would be a function of resistance, as current takes all paths, and that the scenario of simultaneous and equally faulted current to ground is highly unlikely. The moderator also stated that “the GFCI doesn’t measure individual (per leg) current or compute anything”, but “measures the secondary current on the zero sequence CT, and if it’s above a predetermined value based on the turns ratio, the GFCI trips”. I have always thought that the GFCI tracks the magnitude of current directionally, constantly comparing flow to return for equality. He had stated that in support of his saying that the GFCI would measure 0.000A leakage current, if L1 and L2 were simultaneously leaking 2mA each to the EGC. I suspect that the main questions above about length limitations, and single vs double pole performance, are not well understood in the industry, because of the very limited number of comments on my posted question, in a group with 70.8k that typically will have 300-500 comments per post, I think most are awaiting some authentic answers, so many people might be watching this. I sure appreciate your response, Tom! Great live session today too!
Fault Current question. How far down in the power distribution system are we required to calculate fault current?
I have an interesting question that came to me involving a code issue. I have been doing this for many years and it never was brought up. Possibly due to in the old days using the conduit and cable tray system as grounding, but we have since not done that in many years.
The question is do you need an Equipment Grounding Conductor on a motor control circuit to field devices (such as start/stop switches and relays) on a motor control circuit off the CPT on the integral motor starter circuit? Interesting question because usually the field boxes for the switches are plastic and the contacts for the start/stop are plastic with metal screws for the conductors with basically no place for a ground. You essentially would have to screw a locking ring nut to the conduit with a ground lug to find a place to land the ground.
I know the code mentions that a motor control circuit from the CPT is not considered a branch circuit, but not sure if this is relevant. However, there is nothing in the code that I can find that addresses this specifically for motor control circuits, but it may be simply implied that an EGC is needed.
For all of our Q&A Friday sessions, please click here.
TD University
So I’m exploring new things with introducing some educational content through UDEMY. We’ll see how that performs and maybe gets a little funding for the resources I’m bringing to the electrical safety world.
Transformer Protection
This class takes a loot at transformer protection and focuses on two dry-type transformers including a 75kVA and 500kVA transformer example.
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