Should I upsize the wire on a 250ft run?

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mbrooke said:

Electrical safety statistics - Nickle Electrical

About 400 deaths and 4,000 injuries are reported each year due to electrical hazards. Here are a few statistics about electrical safety.
www.nickleelectrical.com www.nickleelectrical.com

GFCIs have helped immensely when 250.4 (5) has fallen short.

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What does electrocutions have to do with fault clearing. Yours talking about the time it takes to clear a fault in a feeder, and the graph you put up references electrocutions and GFCI.
 
There was an interesting Mike holt video about using the 75 degree column to size everything. Also arguing about the residential table back in 2011 that allowed the use of 70% service wire and they moved it to a paragraph. I’ve seen in my short career residential electricians using this in comercial/industrial settings and also in branch circuits or subpanels. The argument Mike was making was if you are selling a 200 amp service then you should give the customer a 200 amp rated wire. Same for a subpanel or a branch circuit.


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mikeames said:
What does electrocutions have to do with fault clearing. Yours talking about the time it takes to clear a fault in a feeder, and the graph you put up references electrocutions and GFCI.
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ActionDave wanted a number of lives lost per year. Granted, there is more than one cause.


When a fault occurs the circuit becomes a restive divider with all grounded objects becoming energized while the faults persists. The longer metal parts remain energized, the greater the danger to human life. For that reason an OCPD must open promptly. Installers, electricians and engineers have a duty to assure an effective ground fault current path. People confuse discretion with selective compliance.
 
I understand, then the data needed would be number of electrocutions specifically when someone was in contact with a conductive metal part bonded to the building electrical system, and ground, all during a fault somewhere in the same buildings electrical system. The voltage between the metal parts and the earth would need to be 30 plus volts. This does not seem likely or common.
 
mikeames said:
I understand, then the data needed would be number of electrocutions specifically when someone was in contact with a conductive metal part bonded to the building electrical system, and ground, all during a fault somewhere in the same buildings electrical system. The voltage between the metal parts and the earth would need to be 30 plus volts. This does not seem likely or common.
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If a ground fault occurs on a 15-20 amp circuit the voltage can easily reach 60 volts.

Less likely than a fault in a power tool or appliances, but large enough that code requires that metal boxes, fixtures, wall switches, panel boards, ect to have an effective ground fault current path. So we can could conclude a fault in the building's wiring system is of reasonable probability.
 
The fault may be 60v but as you said " circuit becomes a restive divider with all grounded objects " so that resistive divider would have a really good chance of having a low impedance. So what would the touch potential be for a person touching ONE grounded object in that resistive divider?

Yes metal boxes are grounded because the lower impedance greatly lowers the danger to the person. Yes a fault is likely in a building. My point is even if a fault occurs in the building and even if the metal parts have a potential on them the impedance of that systems is much lower than the individual touching that system at one point and earth ground.
 
So let me get this straight....

One side has numbers, calculations, graphs, code references and the likes.

The other side has "nuh-uh", "that's stupid", "everybody does it our way", "look at the money"

🙄🙄🙄🙄
 
RRJ said:
There was an interesting Mike holt video about using the 75 degree column to size everything. Also arguing about the residential table back in 2011 that allowed the use of 70% service wire and they moved it to a paragraph. I’ve seen in my short career residential electricians using this in comercial/industrial settings and also in branch circuits or subpanels. The argument Mike was making was if you are selling a 200 amp service then you should give the customer a 200 amp rated wire. Same for a subpanel or a branch circuit.


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Context is everything. Do you think Mike would argue in favor of eliminating all the load diversity allowances in 230 when it comes to calculating the service size? I don't think he would.

As far as a sub panel, if I put 200A wire on a 200A breaker and run it five hundred feet I have not cheated the customer, especially if the connected load is far less than 200A at any given time.
 
James L said:
So let me get this straight....

One side has numbers, calculations, graphs, code references and the likes.

The other side has "nuh-uh", "that's stupid", "everybody does it our way", "look at the money"

🙄🙄🙄🙄
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What calculations and graphs and code references support your opinion that a 100A conductor needs to be put on a 80A breaker.
 
James L said:
So let me get this straight....

One side has numbers, calculations, graphs, code references and the likes.

The other side has "nuh-uh", "that's stupid", "everybody does it our way", "look at the money"

🙄🙄🙄🙄
Click to expand...
I thought we're not supposed to discuss politics here. :giggle:
 
mikeames said:
The fault may be 60v but as you said " circuit becomes a restive divider with all grounded objects " so that resistive divider would have a really good chance of having a low impedance. So what would the touch potential be for a person touching ONE grounded object in that resistive divider?
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60 volts.

120 volts at the transformer spades, 60 volts total drop across the ungrounded conductor in the service drop, feeder and branch circuit. 60 volts drop total across the EGC, feeder EGC (or conduit), and service neutral.

So during a fault in say the outlet box 60 volts will appear to the plumbing.

In reality the plumbing is bonded to the electrical system so the voltage drop across the service neutral will be off set.

So 50 volts might be more realistic.




Yes metal boxes are grounded because the lower impedance greatly lowers the danger to the person. Yes a fault is likely in a building. My point is even if a fault occurs in the building and even if the metal parts have a potential on them the impedance of that systems is much lower than the individual touching that system at one point and earth ground.
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Lower, but not low enough enough to remove all voltage. The purpose of an EGC is not eliminate voltage in a grounded system, but rather facilitate the operation of an OCPD. Once the OCPD opens then voltage at the fault point (and in turn what ever the person is touching) drops to zero.
 
ActionDave said:
Context is everything. Do you think Mike would argue in favor of eliminating all the load diversity allowances in 230 when it comes to calculating the service size? I don't think he would.

As far as a sub panel, if I put 200A wire on a 200A breaker and run it five hundred feet I have not cheated the customer, especially if the connected load is far less than 200A at any given time.
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I could be wrong, but I will argue that a 200A wire will only be rated 200A at less than 160-200ft (ohms law). That’s just my opinion!


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Here are two graphs
ActionDave said:
Thanks. I know how circuits work.
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Excellent!

Then the next part should be easy >>>



1612724402349.png


Current through the body is a function of voltage and skin resistance.

The above graph shows the higher the current, the less time the body can handle it before dangerous physiological effects take place like cardiac arrest or burns. A breaker should trip BEFORE any lasting damage can take place to the body.

The higher the current, the faster a breaker will trip.

The lower the circuit impedance the higher the current across said breaker.

Meaning those arguing for larger wire or a faster opening circuit breaker (80 vs 100amps) have ground to stand on.
 
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