NEC 230.90 (A) EX #3

[etszap]

JUST GOT A RISER DIAGRAM FOR A RESIDENTIAL ADDITION. EXISTING 200 AMP SERVICE. EXISTING PANEL DOESN'T HAVE ENOUGH SPACE FOR ADDITION. RISER SHOWS A TOTAL OF (2) 200 AMP MAINS OUTSIDE (1) FOR EXISTING AND (1) FOR NEW CONNECTED TO EXISTING 200 AMP METER CAN.
DADE COUNTY APPROVED THE DRAWINGS.
I UNDERSTAND THE ARTICLE. I THINK IT IS MORE FOR COMMERCIAL APPLICATIONS WHERE MOTORS, CHILLERS, ETC ARE INVOLVED THAN RESIDENTIAL.
IF A LOT OF THESE GO IN AS DRAWN, IT COULD CREATE A LARGE PROBLEM DOWN THE ROAD WHEN PEOPLE BUY HOT TUBS, ETC.
WHATS THE GENERAL CONSENSUS?
(IN DADE COUNTY IT IS THE CUSTOMERS METER CAN AND RISER- POWER COMPANY RESPONSIBILITY ENDS AT THE CONNECTIONS AT THE WEATHERHEAD)

[ November 05, 2003, 04:59 PM: Message edited by: etszap ]

 

[jerryb]

Re: NEC 230.90 (A) EX #3

I'm going to assume that the meter, socket and service conductors are the property of the utility company. Also I am assuming that the utility has seen this riser and realize that there will be an increase in load.

In most areas, the utility is not governed by the NEC and they provide services based on past history and knowledge of the systems.

I don't think I see the violation or the problem. The utility is required to provide a structure with services capable of handling the load. If the metering and wire end up being too small then they will have to upgrade the system, whether it is at the house, or on the pole, or down the street. Normally we would submit this to the utility for there approval. If there are any utility charges for extra service, that is when they make it known to the owner. The utility is has to be involved at some point, surely they would pull the meter before anyone makes Line-side connections?

 

[iwire]

Re: NEC 230.90 (A) EX #3

Most likely the service conductors are under the control of the NEC.

This installation is still allowed by Exception 3 to 230.90(A) as long as the calculated load does not exceed the conductors rating.

VII. Service Equipment ? Overcurrent Protection
230.90 Where Required.
Each ungrounded service conductor shall have overload protection.

(A) Ungrounded Conductor. Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. A set of fuses shall be considered all the fuses required to protect all the ungrounded conductors of a circuit. Single-pole circuit breakers, grouped in accordance with 230.71(B), shall be considered as one protective device.

Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

I think it is a very strange exception.

I know of a service with 1600 amps of service conductors with 3000 amps of overcurrent protection on it dived among six breakers.

The only thing that prevents it from being overloaded is luck.

When installed the calculated load was under the 1600 amps, now more equipment is being added all the time.

Unless future electricians are careful things will get hot.

[ November 05, 2003, 05:20 PM: Message edited by: iwire ]

 

[websparky]

Re: NEC 230.90 (A) EX #3

Let me see if I understand your description;

(1)Existing 200A sevice.

(2)New 200A service in addition to existing.

(3)One existing 200A meter with both services going to the one meter? How?

 

[iwire]

Re: NEC 230.90 (A) EX #3

Websparky, I am confussed what do you mean how?


One dwelling one "service" with two 200 amp main breaker panels on one 200 amp meter.

RISER SHOWS A TOTAL OF (2) 200 AMP MAINS OUTSIDE (1) FOR EXISTING AND (1) FOR NEW CONNECTED TO EXISTING 200 AMP METER CAN.

Bob

 

[websparky]

Re: NEC 230.90 (A) EX #3

Bob,

I guess I'm confused as to the term "riser". Does it mean a second service drop? If not, then what is the rating of the meter base if you can add two 200A potential loads? What would protect the meter base if the potential is 400A total load?

 

[iwire]

Re: NEC 230.90 (A) EX #3

Dave I think that is exactly what etszap is asking about.

Nothing is protecting the conductors from being overloaded in the future.

Part of Exception 3 to 230.90(A)

The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors

But that seems to be exactly what this exception allows.

It goes right over my head as to the logic of this.

 

[etszap]

Re: NEC 230.90 (A) EX #3

Dave I think that is exactly what etszap is asking about.

That is the gist of the problem. Everyone knows that additional loads can and will be added, especially if there are (2) 200 Amp panels with avaiable breaker spaces.
I cannot believe that the Article was intended for residential use in any fashion.
The customer basically has a 400 Amp service with 200 Amps of service wire and metering.

 

[websparky]

Re: NEC 230.90 (A) EX #3

(IN DADE COUNTY IT IS THE CUSTOMERS METER CAN AND RISER- POWER COMPANY RESPONSIBILITY ENDS AT THE CONNECTIONS AT THE WEATHERHEAD)

Since the utility service ends at the weatherhead, we can most certainly include the mast and metering enclosure in the NEC's jurisdiction. I believe the references below would be applicable.

2002 NEC
110.3 (A) Examination. In judging equipment, considerations such as the following shall be evaluated:
(5) Heating effects under normal conditions of use and also under abnormal conditions likely to arise in service
(7) Classification by type, size, voltage, current capacity, and specific use

(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

 

[jro]

Re: NEC 230.90 (A) EX #3

The right thing to do is upgrade the service to 400 amps and use a 400amp meter base. There is already an exsisting 200 amp panel, adding another 200 amp panel, we all know will have additional loads added to it. Now according to other NEC publications, the exception is permitted when motor loads are present, for example, motors can pull up to six times their full-load running current at start up. In these cases, the OCPD shall be sized to permit the motor to start. A rating higher than the allowable ampacity is permitted, when necessary to handle motor-starting currents

[ November 06, 2003, 12:40 AM: Message edited by: jro ]

 

[iwire]

Re: NEC 230.90 (A) EX #3

The right thing to do is upgrade the service to 400 amps and use a 400amp meter base.

That would be my thought also, but strangely enough it is not required.

Now according to other NEC publications, the exception is permitted when motor loads are present, for example, motors can pull up to six times their full-load running current at start up.

I think that would be Exception 1 to 230.90(A)

230.90(A)Exception No. 1: For motor-starting currents, ratings that conform with 430.52, 430.62, and 430.63 shall be permitted.

I do not see how you can use 110.3(A) or (B) to shoot this down when the code spells out you can do this.

As much as I do not understand the logic for this exception, requiring a 400 amp meter socket in the middle of 200 amp service conductors would not seem to be necessary.

The NEC seems to allow the use of the 200 amp conductors in this case because the calculated load is under 200 amps so a 200 amp meter socket would be fine also.

etszap I do not see anything that limits that exception to any particular occupancy.

Can anyone say why this exception was put into the code or why the example etszap gave should be allowed?

This exception seems to go against everything else in the code about overcurrent protection.

What are the chances that anyone adding load to these panels will recalculate the load to make sure they are still under 200 amps.

[ November 06, 2003, 03:42 AM: Message edited by: iwire ]

 

[chuck miller]

Re: NEC 230.90 (A) EX #3

I would say that the connected load is somwhat less than 400A. The demand load may well be less than 200A.

Chuck Miller

 

[charlie]

Re: NEC 230.90 (A) EX #3

OK, while I tend to agree with some of the reasoning, the Code does not provide for the future. The Code is a book of rules that provides for the practical safeguarding of persons and property from hazards arising from the use of electricity. If you comply with the Code, the installation will be essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use. In other words it is a book of minimums.

A customer can have a safe installation now but not in the future if he adds to it without looking at his system. That is where a qualified electrician comes in and he may well be in trouble if one is not used.

If a DIY, a neighbor, or a jackleg does the work, it could burn or blow up.

 

[jro]

Re: NEC 230.90 (A) EX #3

The NEC seems to allow the use of the 200 amp conductors in this case because the calculated load is under 200 amps so a 200 amp meter socket would be fine also.

What calculated load, all he has is a 200amp service existing, the additional 200amp panel is, as I am reading into this, for future or in progress construction, what needs to be done about this is present this to the architect and explain the concerns and submit a change order, that is?what is done in any job scope, all this guess work will only lead to problems, blueprints are a guide to how the job would need to be done, if there are errors it is expected that the contractor review the prints and bring to light any concerns, and I have caught many errors in blueprints, correcting them now is much better than when all work is complete, then what.This is a residential service, are we saying the load will remain under 200amps forever, from experience I would say no.

 

[iwire]

Re: NEC 230.90 (A) EX #3

This is a residential service, are we saying the load will remain under 200amps forever, from experience I would say no.

I do not think any any of us think a service residential or otherwise will not have increased loads as time goes on.

 

[rb]

Re: NEC 230.90 (A) EX #3

You can't enforce the code based on what someone may do. Assuming that the load calculations are correct the most likely code violations would be the proper termination of the conductors and wire bending space in the meter socket.

It seems unlikely to me that a meter socket designed for 200 amps would have double lugs suitable for No. 3/0 awg conductors.

Ron Bethea

 

[websparky]

Re: NEC 230.90 (A) EX #3

Hi Ron,

I agree that the code can not be enforced for something that someone may do in the future.
However, I believe we as experienced professionals have a duty to bring certain items to the attention of the authorities if we believe that there may be reasonable risk to life and property by not having certain safeguards in place at the time of installation and design.

2002 NEC
90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.
(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

FPN: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes will provide for future increases in the use of electricity.

(C) Intention. This Code is not intended as a design specification or an instruction manual for untrained persons.

Would we not be remiss if some time in the future a situation like this attributed to the loss of life?