Transformer install - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Trade Topics > NEC Code Forum


Reply
 
Thread Tools Display Modes
Old 09-08-2016, 02:13 AM   #1
Senior Member
 
Arrow3030's Avatar
 
Join Date: Mar 2014
Location: California
Posts: 128
Rewards Points: 122
Default Transformer install

I'm looking for validation. I'll list disputed areas related to my particular project numerically.

1) A Delta/Wye transformer requires an OCPD on the secondary.
2) The secondary OCPD is allowed to be 125% the value of the transformer name plate. Next standard size allowed.
3) The secondary conductors must have an allowable ampacity greater than or equal to the secondary OCPD.
4) The allowable ampacity of the primary conductors must be greater than or equal to the rating of the transformer.
5) The primary OCPD is allowed to be 250% the value of the transformer name plate. Next standard size allowed.

*No continuos loads

6) Why did the dude before me try to tripple tap an outdoor transformer, bring the secondary cond's in the building with no OCPD, continue the run indoor for 50,75 & 100' respectively and terminate in three main lug load centers?
Arrow3030 is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 09-08-2016, 05:26 AM   #2
Semper Fidelis
 
Suncoast Power's Avatar
 
Join Date: Jan 2009
Location: Florida
Posts: 13,302
Rewards Points: 4,256
Default

Certainly you have a problem.
Is this a farm?
Suncoast Power is offline   Reply With Quote
Old 09-08-2016, 08:45 AM   #3
Senior Member
 
Arrow3030's Avatar
 
Join Date: Mar 2014
Location: California
Posts: 128
Rewards Points: 122
Default

Not a farm
Arrow3030 is offline   Reply With Quote
Old 09-08-2016, 09:43 AM   #4
animal lover /rat bastard
 
wildleg's Avatar
 
Join Date: Apr 2009
Location: somewhere in FL
Posts: 12,326
Rewards Points: 384
Default

Quote:
Originally Posted by Arrow3030 View Post
I'm looking for validation. I'll list disputed areas related to my particular project numerically.

1) A Delta/Wye transformer requires an OCPD on the secondary.
2) The secondary OCPD is allowed to be 125% the value of the transformer name plate. Next standard size allowed.
3) The secondary conductors must have an allowable ampacity greater than or equal to the secondary OCPD.
4) The allowable ampacity of the primary conductors must be greater than or equal to the rating of the transformer.
5) The primary OCPD is allowed to be 250% the value of the transformer name plate. Next standard size allowed.

*No continuos loads

6) Why did the dude before me try to tripple tap an outdoor transformer, bring the secondary cond's in the building with no OCPD, continue the run indoor for 50,75 & 100' respectively and terminate in three main lug load centers?

there are a lot of rules, as well as exceptions to the rules, in 450. You need to provide a little more information: are these services ? is the transformer owned by the poco ? are the conduits into the building underground or encased ? are the panels main breaker ? 450 has all the answers except the ones relating to the service, by the numbers, but if you provide a little more info your questions are easy to answer.
__________________
this message was sent from a dental floss farm using ZappaTalk and a pair of zirconium encrusted tweasers
wildleg is offline   Reply With Quote
Old 09-08-2016, 10:00 AM   #5
Senior Member
 
Join Date: Jul 2010
Location: IL
Posts: 3,823
Rewards Points: 1,212
Default

Quote:
Originally Posted by Arrow3030 View Post
I'm looking for validation. I'll list disputed areas related to my particular project numerically.

1) A Delta/Wye transformer requires an OCPD on the secondary.
2) The secondary OCPD is allowed to be 125% the value of the transformer name plate. Next standard size allowed.
3) The secondary conductors must have an allowable ampacity greater than or equal to the secondary OCPD.
4) The allowable ampacity of the primary conductors must be greater than or equal to the rating of the transformer.
5) The primary OCPD is allowed to be 250% the value of the transformer name plate. Next standard size allowed.

*No continuos loads

6) Why did the dude before me try to tripple tap an outdoor transformer, bring the secondary cond's in the building with no OCPD, continue the run indoor for 50,75 & 100' respectively and terminate in three main lug load centers?
Item 4 is not correct. The ampacity of the primary conductors must be equal to or greater than the OCPD that supplies them.
There are no provisions in either Article 240 or 450 that permit the primary conductors to be connected to an OCPD that has a rating greater than the ampacity of the conductors.
don_resqcapt19 is offline   Reply With Quote
The Following User Says Thank You to don_resqcapt19 For This Useful Post:
Arrow3030 (09-08-2016)
Old 09-08-2016, 10:09 AM   #6
Senior Member
 
Arrow3030's Avatar
 
Join Date: Mar 2014
Location: California
Posts: 128
Rewards Points: 122
Default

Not a service.

Customer owned transformer.

Conduits are underground to the building then continue in emt inside the building.

No discos on the secondary (feeds into main lug panels, not main breaker)
Arrow3030 is offline   Reply With Quote
Old 09-08-2016, 10:13 AM   #7
Senior Member
 
Join Date: May 2015
Location: Sacramento, California
Posts: 7,032
Rewards Points: 12,340
Default

An out door transformer makes one think in terms of underground secondaries terminating at OCPD within each panel.

Is such the case, here ?
telsa is offline   Reply With Quote
Old 09-08-2016, 10:21 AM   #8
Senior Member
 
Arrow3030's Avatar
 
Join Date: Mar 2014
Location: California
Posts: 128
Rewards Points: 122
Default

Nope. Previous electrician was planning to feed main lug panels with no secondary OCPD. The line diagram would go primary OCPD to transformer to three main lug load centers.
Arrow3030 is offline   Reply With Quote
Old 09-08-2016, 12:46 PM   #9
Semper Fidelis
 
Suncoast Power's Avatar
 
Join Date: Jan 2009
Location: Florida
Posts: 13,302
Rewards Points: 4,256
Default

Quote:
Originally Posted by Arrow3030 View Post
Not a farm
Ok then. You have to correct it.
Suncoast Power is offline   Reply With Quote
The Following User Says Thank You to Suncoast Power For This Useful Post:
Arrow3030 (09-08-2016)
Old 09-08-2016, 02:16 PM   #10
Senior Member
 
Arrow3030's Avatar
 
Join Date: Mar 2014
Location: California
Posts: 128
Rewards Points: 122
Default

Right on, thanks. My plan for the secondary is to come into a main breaker panel at the point of entry. Then use feeders out of that to the main lug subs. This is my first real world transformer so I appreciate everyone's help.

I'll size the primary OCPD to 125% the trans and use a conductor with greater or equal allowable ampacity.

I'll size my secondary to 125% the transformer and use conductors with equal or greater ampacity.

What I don't understand is why I'd want to size the primary to 250%. That seems wasteful since the conductors have to be sized to the OCPD. Anyone have insight on why using a higher percentage on the primary vs the secondary is beneficial?
Arrow3030 is offline   Reply With Quote
Old 09-08-2016, 03:15 PM   #11
Modérateur
 
frenchelectrican's Avatar
 
Join Date: Mar 2007
Location: Philippines { for a while }
Posts: 5,784
Rewards Points: 628
Default

Quote:
Originally Posted by Arrow3030 View Post
Right on, thanks. My plan for the secondary is to come into a main breaker panel at the point of entry. Then use feeders out of that to the main lug subs. This is my first real world transformer so I appreciate everyone's help.

I'll size the primary OCPD to 125% the trans and use a conductor with greater or equal allowable ampacity.

I'll size my secondary to 125% the transformer and use conductors with equal or greater ampacity.

What I don't understand is why I'd want to size the primary to 250%. That seems wasteful since the conductors have to be sized to the OCPD. Anyone have insight on why using a higher percentage on the primary vs the secondary is beneficial?

The most common curpit is inrush current that one of few reason why the OCPD is set for max of 250% .,,

It work both ways in upstep or downstep fashion., but keep in your mind the upstep verison is harder so expect more inrush current when first engerized it.,
__________________
Bleu est beau.
frenchelectrican is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Transformer neutral bond sizing (paralleled secondary) haltonelectrician Canadian Electrical Code Forum 27 06-19-2016 06:21 PM
3 phase transformer single phase supply Ultrafault General Electrical Discussion 24 06-12-2016 11:47 AM
has anyone ever install a 120/208 to 347/600 transformer? mike883 General Electrical Discussion 7 05-14-2016 10:08 AM
Transformer Bonding CES Services and Service Equipment 25 04-22-2016 11:54 PM
Can SDGE require my customer to pay for transformer Jeremy9 General Electrical Discussion 7 04-07-2016 06:01 PM


All times are GMT -4. The time now is 01:52 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com