Main disconnect on building for 2020?

don_resqcapt19

Moderator
Staff member
In cold environments, thermal magnetic breakers will carry more current, is that what you are referring to? But for the most part the 'up North here' nobody takes the characteristics into consideration. There are thousands of multi-metering applications installed where no adjustments have been required.


The emergency disconnect, like the meter disconnect, probably would not need to be rated to close into a fault condition, and may not even need to break bolted fault conditions, unlike a service disconnecting means.
Why don't we take that into account? How is a breaker that trips 25% higher than nameplate for at least 5 months of the year, in my area, a code compliant installation?
 

jim dungar

Moderator
Staff member
Why don't we take that into account? How is a breaker that trips 25% higher than nameplate for at least 5 months of the year, in my area, a code compliant installation?
Based on the lack of any significant number of reported issues with this type of installation, I would guess the NEC tables for conductor sizing are sufficiently conservative and therefore the overcurrent protective device performance is satisfactory.

In my locale, the outdoor breaker are almost always, like 300 days/year, under 40°C . In fact, they may hardly often even exceed 25°C, for more than 3 hours at a time, unless they are are south facing.
 

ggunn

PE (Electrical), NABCEP certified
Why don't we take that into account? How is a breaker that trips 25% higher than nameplate for at least 5 months of the year, in my area, a code compliant installation?
Doesn't conductor ampacity also increase under those conditions?
 

don_resqcapt19

Moderator
Staff member
Doesn't conductor ampacity also increase under those conditions?
It code permitted increase is not as much as the increase in the trip point. The maximum multiplier in 310.15(B)(2)(a) is 1.15. Also, in many cases only a very small part of the conductor run is outside. Square D shows a 25% shift for their larger breakers in a 50°F ambient. While there would be some slight increase in the interior of the enclosure, I expect that in my area, a single main breaker in an exterior enclosure would operate at or below 50°F for about 5 months of the year.

The shift is even worse for some smaller breakers. It appears to me that a 25°C (77°F) can place the long term trip at 2x breaker rating.
 

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jim dungar

Moderator
Staff member
Don,

For derating purposes, you need to find the temperature derating curves and not simply shift the standard TCC. Use their publication called "Current Carrying Capacity In Special Applications" (0100DB0101).

At 0°C:
QOT 20A trips around 22A,
QO 20A trips around 26A
QOM100A trips around 125A
QOM 200 trips around 260A
 

don_resqcapt19

Moderator
Staff member
Don,

For derating purposes, you need to find the temperature derating curves and not simply shift the standard TCC. Use their publication called "Current Carrying Capacity In Special Applications" (0100DB0101).

At 0°C:
QOT 20A trips around 22A,
QO 20A trips around 26A
QOM100A trips around 125A
QOM 200 trips around 260A
Jim,
And that shows a 25% increase in the trip for the larger breakers. However the SquareD document that I have shows the 25% increase at 10°C, not zero. The document is titled "Determining Current Carrying Capacity in Special Applications", but has the same publication number. How is a 25% increase in the trip for 5/12s of the year code compliant? As far as their smaller breakers what does the dotted line to the right that is titled "maximum trip times at 25°C" mean. To me is says that the maximum trip time at that temperature is much higher than the breaker rating.
 

jim dungar

Moderator
Staff member
Don,

My copy of this publication is from July 1988 (#SD361 R1) and has the same curves as the link I provided.

The dashed lines on the trip curve should be based on the NEMA standard AB-2 for a single pole breaker, rather than on the actual breaker. This is probably a worse case 'long time delay', but honestly, I have never seen a clear explanation of when/how this reference would be used.
 

don_resqcapt19

Moderator
Staff member
Don,

My copy of this publication is from July 1988 (#SD361 R1) and has the same curves as the link I provided.

The dashed lines on the trip curve should be based on the NEMA standard AB-2 for a single pole breaker, rather than on the actual breaker. This is probably a worse case 'long time delay', but honestly, I have never seen a clear explanation of when/how this reference would be used.
Jim,
The document I am looking at for the larger breakers is "Determining Current Carrying Capacity in Special Applications Data Bulletin 0100DB0101"dated 06/01. That document also seems to say that you can't even use those breakers where the ambient temperature at the breaker would fall be low -10°C (14°F).
Square D circuit breakers can be applied in ambient temperatures within the range of -10°C to 60°C (14°F to 140°F). This document provides guidelines to follow when adjusting for ambient conditions.
UL has told me that this is a 110.3(B) instruction and prohibits the installation of the breaker in an outside location in my area.

As far as the dashed line, we just ignore it? How is the dashed line different from the 40°C trip band on the same trip curve?

I think that the temperature sensitiviy of thermal magnetic breakers is just something that has been ignored for a long time. Maybe there are no real issues with the trip change, but I can see cases where it could have an impact. If I worked for Leviton, I would be pushing this issue. They use "hydraulic" breakers that are not temperature sensitive. However that has a cost impact and is one of the reasons why their panels are more expensive.
 

jim dungar

Moderator
Staff member
How is the dashed line different from the 40°C trip band on the same trip curve?
The dashed line is not a characteristic of the breaker shown in the TCC. It is representative of a generic worst case device.

I can't think of any breaker that would not be somewhat affected by temperatures below 14°F. Many greased mechanism parts tend to be sluggish at 'negative' temperatures.
 

don_resqcapt19

Moderator
Staff member
The dashed line is not a characteristic of the breaker shown in the TCC. It is representative of a generic worst case device.

I can't think of any breaker that would not be somewhat affected by temperatures below 14°F. Many greased mechanism parts tend to be sluggish at 'negative' temperatures.
So we shouldn't use breakers outside where it gets cold. With the emergency disconnect rule, I think we will see a lot more outside service overcurrent protective devices. Maybe an Informational Note should be added to 230.85.
 

jim dungar

Moderator
Staff member
So we shouldn't use breakers outside where it gets cold.
I didn't say that.

Our industry has 50+ years of outdoor breaker installation history, particularly with multi-meter centers. I have no significant amount anecdotal evidence of outdoor breakers not offering appropriate protection except when they overheat in sunshine.
 

Coppersmith

Senior Member
I was talking to an inspector from my area yesterday and he mentioned there may be a new requirement to have a main service disco on the residence(outside, on side of building) for 2020. Presumably for first response reasons but I don't know for sure. Anyone know more about this?
If the circuit breaker panel is located outside and has a main breaker, can this main breaker serve as the above mentioned main service disco?
 

Coppersmith

Senior Member
The cold breaker problem being discussed could be solved by adding a heater to an outdoor panel. This is not a problem in my area however since it's still about 60F outside in January. We would have to opposite problem. A sun-heated outdoor panel may cause breakers to trip too soon. Dedicated breaker panel a/c systems are too expensive although venting indoor air into it may be possible.
 

ActionDave

Moderator
Staff member
If the circuit breaker panel is located outside and has a main breaker, can this main breaker serve as the above mentioned main service disco?
Yes. Pretty much a standard set up here where I live and has been that way for about forty years.
 

Strombea

Member
I think a pair of dykes to cut the poco meter tag and then simply pulling the meter is better than actual discos, most people put padlocks on Mains anyway so pulling meter is probably quicker
 

don_resqcapt19

Moderator
Staff member
I didn't say that.

Our industry has 50+ years of outdoor breaker installation history, particularly with multi-meter centers. I have no significant amount anecdotal evidence of outdoor breakers not offering appropriate protection except when they overheat in sunshine.
But I did say that and the manufactures publications are 110.3(B) instructions. Just because we have not had seen problems does not mean there is not a code violation.
 
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