The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Safety at heights?
by Trumpy
Today at 05:25 AM
Old Bath Fan
by gfretwell
Today at 01:38 AM
Search Function
by Webmaster
Yesterday at 11:13 PM
Forum Software Upgrade coming soon...
by Webmaster
Yesterday at 09:17 PM
ESA Arc flash course
by frank
Yesterday at 04:25 PM
New in the Gallery:
Desk-mounted "power-board"
Top Posters (30 Days)
Webmaster 30
HotLine1 21
Ruben Rocha 16
gfretwell 13
Trumpy 13
Who's Online
1 registered (electure), 0 Guests and 181 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#57614 - 10/17/05 12:24 PM corner tapped delta
lamplighter Offline
Member

Registered: 10/05/05
Posts: 101
Loc: Clawson,Michigan,USA
I've only had to work with this a couple of times but, in each time, I got different answers from those that seemed "in the know".
When installing a disconnect on the secondary side of a corner tapped delta transformer, does one need to fuse the grounded leg or install a dummy fuse in the jaws?
I've been told to fuse it since it is one of the three legs going to the equipment but, it's also the grounded conductor which would mean NO FUSE.
I can't find anything in the code about this.
Any help?

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#57615 - 10/17/05 12:43 PM Re: corner tapped delta
Crowbar Offline
Member

Registered: 01/13/03
Posts: 34
Loc: Pittsburgh, PA,USA
Being an intentionally grounded conductor would make 240.22 (2002 NEC) apply
"No overcurrent device shall be connected in series with any conductor that is intentionally grounded, unless"...(exceptions not relevant in this case)

Top
#57616 - 10/17/05 06:16 PM Re: corner tapped delta
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Ditto crowbar.

A grounded conductor by any other name (neutral, or not) is a grounded conductor.
Don't forget Article 200.



[This message has been edited by Redsy (edited 10-17-2005).]

Top
#57617 - 10/17/05 07:05 PM Re: corner tapped delta
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
I beg to differ! On a corner grounded delta you most certainly fuse the grounded leg!
See 430.36, which specifically addresses this situation.

Top
#57618 - 10/17/05 07:35 PM Re: corner tapped delta
gfretwell Offline


Member

Registered: 07/20/04
Posts: 9063
Loc: Estero,Fl,usa
Reno, that is only if the fuses are the "overload" protection. That does not affect the OC device for overcurrent protection.
_________________________
Greg Fretwell

Top
#57619 - 10/18/05 03:33 PM Re: corner tapped delta
ShockMe77 Offline
Member

Registered: 06/11/05
Posts: 823
Loc: Rahway, New Jersey
430.36 says: and also in the grounded conductor if the supply system is a 3-wire, 3 phase ac with one conductor grounded.

I'm not an expert of Delta systems, but this code in my opinion says yes, the grounded conductor must have fused protection.

[This message has been edited by ShockMe77 (edited 10-18-2005).]

Top
#57620 - 10/18/05 04:18 PM Re: corner tapped delta
togol Offline
Member

Registered: 09/15/05
Posts: 426
Loc: NW In. USA
...mind if I jump in and ask... if there are any problems with two-wire single phase loads? should I not use the grounded phase on a two pole breaker ?
its been years since I worked on this type of service and I have a job moving a small shop with a single phase service to an old building with ths stuff ?
I realize I need to check the motors that are running off of converters, I just ain't sure about the 2 pole gear
_________________________
Tom

Top
#57621 - 10/18/05 04:29 PM Re: corner tapped delta
earlydean Offline
Member

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
Read the whole section:

"430.36 Fuses — In Which Conductor.
Where fuses are used for motor overload protection, a fuse shall be inserted in each ungrounded conductor and also in the grounded conductor if the supply system is 3-wire, 3-phase ac with one conductor grounded."

There is a difference between overload protection and short circuit and ground fault protection. Motors circuits break the overcurrent protection into these two parts:
1) Short circuit and ground fault protection
2) Overload protection

We usually provide #1 with the circuit breaker protecting the feeder, and #2 with heaters in the motor starter.

At a transformer providing power to a motor control center, all the conductors need to follow the rules in Article 240.

"II. Location
240.20 Ungrounded Conductors.
(A) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor."

"240.21 Location in Circuit.
Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply except as specified in 240.21(A) through (G)."

And most importantly:

"240.22 Grounded Conductor.
No overcurrent device shall be connected in series with any conductor that is intentionally grounded, unless one of the following two conditions is met:
(1) The overcurrent device opens all conductors of the circuit, including the grounded conductor, and is designed so that no pole can operate independently.
(2) Where required by 430.36 or 430.37 for motor overload protection."

Fuses cannot simultaneously open all conductors of the circuit. That leaves us only (2).

The answer, then, is: unless the fuse is intended to provide the overload protection for a motor (instead of the heaters) then a fuse in the grounded conductor is not allowed. So, go ahead, install a two pole fused disconnect for your motor control center.

Does the listing on a three phase disconnect permit the installation of a six inch piece of copper pipe in place of a fuse? Or, does the manufacturer sell dummy fuses for this purpose? Or is it only proper to install a 2 pole fused disconect for this use?
_________________________
Earl

Top
#57622 - 10/18/05 04:59 PM Re: corner tapped delta
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA

Top


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals