ECN Forum Forums General Topics of the Trade General Discussion Area Ask me anything?

6-6-98
Somebody asked the question about the three switches in the basement and the light bulb in the attic.
Here is the answer: RAY: You turn the first switch on. You leave it on for ten minutes. Why, you ask? You'll see in a minute. Then you turn it off and you turn the second switch on and you go upstairs.

This is an old puzzler from CarTalk.com with Tom and Ray, the tappit brothers. Look under puzzler and archives. These are pretty good.
~Peter

Thats a good one, anyone else have anymore like that?

Q:"What is the minimum size conductor needed to connect the secondary of a transformer to a panel with a 400 amp main breaker."

A:600 kcmil thhn @75c is good for 420amp.
But two paralleled 3/0 is good for 400amp.

i'm i missing something?

Bucketman
You did no miss a thing. You are right on.
The reason I asked this question was because there was some confusion on another forum regarding 240.3B and transformer secondary.
Some felt that 500 kcm was the minimum size.
However 240.20C requires the ampacity of the conductor to match the OC device.

[This message has been edited by Bob (edited 01-16-2005).]

Q:"Which of these Seperately Derived Systems (SDS) may use the OCPD on the Primary side to protect the Secondary side feeders - and why?"

A: (A)
240.(C)(1) & 450.3 (B)

Q:"Which of these Seperately Derived Systems (SDS) may use the OCPD on the Primary side to protect the Secondary side feeders - and why?"


I was thinking "A", "B" and "E" would qualify, as they all have a "Single" Secondary Output Voltage", whereas "C", "D" and "F" would nt qualify, as they have Multiwire Secondaries.

Scott35

Since you're still going at it.

Someone asked me: "where in the NEC does it say I must use MC to hardwire a disposal"?

Q:" Someone asked me: "where in the NEC does it say I must use MC to hardwire a disposal"?

A: 422.16 (B)(1)
this is the only specific this I found on disposals
you should also be able to use flex.

Well I'm 3000 miles from the east coast, but in an easterly direction. Not sure whether that makes me very friendly or a real grouch!

Which begs the question: What is the difference between gray and natural gray?

Naw, Pauluk it just means your even further West than I am. Hey, only kidding around about the regional "Nice Guy" thing. Just a friendly poke.