240V Receptacle to breaker matching

Status
Not open for further replies.
R

RFEngineer

Member
Just when I need my 2008 NEC book, it eludes me...

I presently have a branch circuit with 10/4 cabling, a 30A double-pole breaker, and a 30A L14-30R (250V/125V) receptacle that serves an electronic equipment rack. 30A is well over-rated for the acrtual use. I am going to start using a UL-compliant 240V RPT that is limited to 20A connectors per UL RPT guidelines. Here's my question:

If I change the serving wall receptacle to a single 20A L14-20R, must the serving breaker also be rated 20A or may I leave the existing 30A breaker? My gut tells me NEC will require alignment of a 20A breaker for use with a single 20A receptacle. Gut right or wrong? Tnx!

Paul
 
T

templdl

Senior Member
Location
Wisconsin
RFEngineer said:
Just when I need my 2008 NEC book, it eludes me...

I presently have a branch circuit with 10/4 cabling, a 30A double-pole breaker, and a 30A L14-30R (250V/125V) receptacle that serves an electronic equipment rack. 30A is well over-rated for the acrtual use. I am going to start using a UL-compliant 240V RPT that is limited to 20A connectors per UL RPT guidelines. Here's my question:

If I change the serving wall receptacle to a single 20A L14-20R, must the serving breaker also be rated 20A or may I leave the existing 30A breaker? My gut tells me NEC will require alignment of a 20A breaker for use with a single 20A receptacle. Gut right or wrong? Tnx!

Paul
Click to expand...
Why the #10? Is it being used because of voltage drop?
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
210.21(B) A single recept shall have a rating not less than the branch circut (OCP)
 
T

templdl

Senior Member
Location
Wisconsin
RFEngineer said:
Just when I need my 2008 NEC book, it eludes me...

I presently have a branch circuit with 10/4 cabling, a 30A double-pole breaker, and a 30A L14-30R (250V/125V) receptacle that serves an electronic equipment rack. 30A is well over-rated for the acrtual use. I am going to start using a UL-compliant 240V RPT that is limited to 20A connectors per UL RPT guidelines. Here's my question:

If I change the serving wall receptacle to a single 20A L14-20R, must the serving breaker also be rated 20A or may I leave the existing 30A breaker? My gut tells me NEC will require alignment of a 20A breaker for use with a single 20A receptacle. Gut right or wrong? Tnx!

Paul
Click to expand...

Since my question was ignored I am to assume then that the is no specific reason that #10 was installed. As such you could use a 20a or even a 15a OCPD. So selecting a 20a OCPD would seem appropriate.
 
C

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
templdl said:
Since my question was ignored I am to assume then that the is no specific reason that #10 was installed. As such you could use a 20a or even a 15a OCPD. So selecting a 20a OCPD would seem appropriate.
Click to expand...

#10 was installed because it is the minimum size required to supply the existing 30 amp receptacle protected by a 30 amp circuit breaker. The OP is asking about changing the receptacle on this existing 30 amp circuit to a lower rating.
 
Little Bill

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
templdl said:
Why the #10? Is it being used because of voltage drop?
Click to expand...

RFEngineer said:
Two reasons: (1) it's pre-existing cable; and (2) the run is long enough that the IR drop could be an issue for 30A service but not 20A service.

Paul
Click to expand...

templdl said:
Since my question was ignored I am to assume then that the is no specific reason that #10 was installed. As such you could use a 20a or even a 15a OCPD. So selecting a 20a OCPD would seem appropriate.
Click to expand...

You may have choice to ignor the answer but the question wasn't ignored.:p
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
RFEngineer said:
Just when I need my 2008 NEC book, it eludes me...

I presently have a branch circuit with 10/4 cabling, a 30A double-pole breaker, and a 30A L14-30R (250V/125V) receptacle that serves an electronic equipment rack. 30A is well over-rated for the acrtual use. I am going to start using a UL-compliant 240V RPT that is limited to 20A connectors per UL RPT guidelines. Here's my question:

If I change the serving wall receptacle to a single 20A L14-20R, must the serving breaker also be rated 20A or may I leave the existing 30A breaker? My gut tells me NEC will require alignment of a 20A breaker for use with a single 20A receptacle. Gut right or wrong? Tnx!

Paul
Click to expand...

Code aside what would be the point of reducing the receptacle rating without reducing the overcurrent device?
 
T

templdl

Senior Member
Location
Wisconsin
What does it take to simply replace the breaker with a 20a and call it a day? What is the panel type? A 20a2p breaker I wouldn't think would break the bank.
 
R

RFEngineer

Member
templdl said:
Since my question was ignored I am to assume then that the is no specific reason that #10 was installed. As such you could use a 20a or even a 15a OCPD. So selecting a 20a OCPD would seem appropriate.
Click to expand...

Hmmm...I thought it was answered in my post above. Maybe it didn't post in time:

"Two reasons: (1) it's pre-existing cable; and (2) the run is long enough that the IR drop could be an issue for 30A service but not 20A service."

Re-cap:

The #10/4 was existing and being used with a 30A OCPD and a 30A L14-30R. A new RPT is being constructed to the UL 1363 standard. But UL 1363 limits an RPT to no more than 20A distribution and all connectors must be of the same current rating. So, it became a domino effect. The RPT has a L14-20P on one side and three L14-20R pig-tails on the opposite side. Various equipment plug into these pig-tails. Since the wall receptacle must now be a L14-20R, then NEC 210.21(B) requires a matching of the OCPD rating as moderator Augie47 points out.

So, UL 1363 limited me to 20A on the RPT and that has a trickle-down (trickle-up?) effect on the premise distribution. The 20A distribution on the branch through the RPT is adequate to power the equipment rack. Again, the 30A service was existing and had significant excess current capacity for the application. Using the RPT in effect forced a re-design of the entire branch, except for the 10/4 cabling.

Many thanks to all for an engaging discussion!

Paul
 
Last edited:
kwired

kwired

Electron manager
Location
NE Nebraska
RFEngineer said:
Hmmm...I thought it was answered in my post above. Maybe it didn't post in time:

"Two reasons: (1) it's pre-existing cable; and (2) the run is long enough that the IR drop could be an issue for 30A service but not 20A service."

Re-cap:

The #10/4 was existing and being used with a 30A OCPD and a 30A L14-30R. A new RPT is being constructed to the UL 1363 standard. But UL 1363 limits an RPT to no more than 20A distribution and all connectors must be of the same current rating. So, it became a domino effect. The RPT has a L14-20P on one side and three L14-20R pig-tails on the opposite side. Various equipment plug into these pig-tails. Since the wall receptacle must now be a L14-20R, then NEC 210.21(B) requires a matching of the OCPD rating as moderator Augie47 points out.

So, UL 1363 limited me to 20A on the RPT and that has a trickle-down (trickle-up?) effect on the premise distribution. The 20A distribution on the branch through the RPT is adequate to power the equipment rack. Again, the 30A service was existing and had significant excess current capacity for the application. Using the RPT in effect forced a re-design of the entire branch, except for the 10/4 cabling.

Many thanks to all for an engaging discussion!

Paul
Click to expand...
Because you changed the receptacle to one of a lower rating you must also change the overcurrent device.

If you changed the overcurrent device only, I don't see much problem with having a 30 amp device on a 20 amp circuit.

If there is more than 20 amps of load then you need either the 30 amp circuit or multiple smaller circuits.
 
Status
Not open for further replies.
Top