Line/load side of equipment

[mstrlucky74]

Is there an easy way to tell line/load side of equipment. I know what it is but sometimes when looking at a riser where you have a pipe run and there's an ats, disconnect transformer etc. in same run it gets confusing. Thanks

 

[teufelhounden91]

Line/load side of equipment

With the equipment open or closed? Looking at the inside of a disconnect you can tell by the blades which side is line and which is load. But looking from the outside there's know way of knowing which direction it goes unless you follow the conduit to where it comes from/goes.


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[Smart $]

In vertically oriented equipment, the line side is typically on top, load side on bottom... in general (NEMA convention usually dictates).

Some equipment can be connected either way, but those that cannot are typically marked Line and Load, some L1, L2, etc. for Line side and T1,T2, etc. Again the marking will be dictated by the standard to which it is manufactured and listed.

In light of recent discussion in another thread, take the preceding with a grain of salt.

 

[Carultch]

Some equipment can be connected either way, but those that cannot are typically marked Line and Load, some L1, L2, etc. for Line side and T1,T2, etc. Again the marking will be dictated by the standard to which it is manufactured and listed.

Open blade disconnects are an interesting counterexample. They are marked line and load, and are also listed for current flow in either direction (not that there is any physics inside to make them direction sensitive). It is best to connect line to the side that remains energized in the open position.

 

[iwire]

Open blade disconnects are an interesting counterexample. They are marked line and load, and are also listed for current flow in either direction (not that there is any physics inside to make them direction sensitive). It is best to connect line to the side that remains energized in the open position.

I cannot connect the line side to the load side if it's marked.

I also must wire fused switches so the the fuses are dead when the disconnect is off

 

[Carultch]

I cannot connect the line side to the load side if it's marked.

I also must wire fused switches so the the fuses are dead when the disconnect is off

My point is that unlike a breaker marked line/load, current can flow in both directions thru a blade disconnect, even though it is marked line/load. It is the voltage energization side that defines which side is the line side, rather than the origin of current flow.

In a breaker marked line/load, both the voltage energization and the origin of current must both be on the line side.

 

[GoldDigger]

One or the other side of the knife switch disconnect will always be hot when the switch is open. The standard design is to have the blades on the load side to minimize the amount of exposed metal on the line side.
Only important if it is an open handle knife switch or you plan on working inside the enclosure of the open disconnect.

 

[GoldDigger]

My point is that unlike a breaker marked line/load, current can flow in both directions thru a blade disconnect, even though it is marked line/load. It is the voltage energization side that defines which side is the line side, rather than the origin of current flow.

In a breaker marked line/load, both the voltage energization and the origin of current must both be on the line side.

So the current can only flow in one direction on a closed case breaker? That is news to me.
And if voltage source and current source must be on the same side you cannot use a line/load marked breaker as an AC disconnect on a GTI in either orientation?
You have me confused.

 

[iwire]

My point is that unlike a breaker marked line/load, current can flow in both directions thru a blade disconnect, even though it is marked line/load.

I am not seeing your point.

Current can flow both directions through a breaker marked line and load as well but in either case for me to hook them up like that is a violation.

 

[ggunn]

I cannot connect the line side to the load side if it's marked.

I also must wire fused switches so the the fuses are dead when the disconnect is off

For a PV system AC disco between an inverter and the service, it's murky. Under normal operation current flows from the inverter and the service is the load, but if you wire the service to the load side of the switch the fuses are hot when you open the switch. You must consider the inverter the load even though the current is flowing in the opposite direction.

According to a couple of inspectors I have spoken with, connecting the AC disco the wrong way around is by far the most common wiring error they encounter in inspecting PV systems.

 

[iwire]

For a PV system AC disco between an inverter and the service, it's murky. Under normal operation current flows from the inverter and the service is the load, but if you wire the service to the load side of the switch the fuses are hot when you open the switch. You must consider the inverter the load even though the current is flowing in the opposite direction.

I have installed PV systems, I understand.

According to a couple of inspectors I have spoken with, connecting the AC disco the wrong way around is by far the most common wiring error they encounter in inspecting PV systems.

Exactly.

 

[big john]

Is there an easy way to tell line/load side of equipment...

You can make a lot of assumptions: Line is usually the top of switches, the top of fuses, primary of transformers (small conductors), the side with the controls/metering connected to it.

But I wouldn't want to count on any of that being true for certain unless you like unpleasant surprises.

 

[Smart $]

...In a breaker marked line/load, both the voltage energization and the origin of current must both be on the line side.

Here's the low down on that situation.

Per UL 489 Paragraph 9.1.1.13: Circuit breakers shall be marked
“Line” and “Load” unless the construction and test results are
acceptable with the line and load connections reversed.


This marking requirement specifies that UL Listed circuit breakers
and molded case switches shall be marked with the word “Line”
on one end of the circuit breaker and the word “Load” on the other
end, as shown in Figure 3, if they are unable to successfully meet
the reverse-feed test requirements per Paragraph 7.1.1.18 of UL
489. Conversely, a UL Listed circuit breaker does not have to be
marked with “Line” and “Load” if it successfully meets the reversefeed
test requirements.

Source: http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/pu01200001e.pdf

 

[iwire]

Is there an easy way to tell line/load side of equipment. I know what it is but sometimes when looking at a riser where you have a pipe run and there's an ats, disconnect transformer etc. in same run it gets confusing. Thanks

The real answer here is experience and a tester.

 

[mstrlucky74]

You can make a lot of assumptions: Line is usually the top of switches, the top of fuses, primary of transformers (small conductors), the side with the controls/metering connected to it.

But I wouldn't want to count on any of that being true for certain unless you like unpleasant surprises.

Primary is always small conductors? What if it's a step down xfrmr?

 

[Smart $]

Primary is always small conductors? What if it's a step down xfrmr?

Most are step down, and the primary would be the smaller conductors compared to the secondary conductors for typical installations, but not all.

Typical conductor sizing is reversed for STEP UP transformers.

 

[ggunn]

Most are step down, and the primary would be the smaller conductors compared to the secondary conductors for typical installations, but not all.

Typical conductor sizing is reversed for STEP UP transformers.

That depends on what you call the primary/secondary. Some folks call the higher voltage side of the transformer the primary irrespective of the direction of current flow. Larger conductors are typically (always?) on the lower voltage side.

 

[Smart $]

That depends on what you call the primary/secondary. Some folks call the higher voltage side of the transformer the primary irrespective of the direction of current flow. Larger conductors are typically (always?) on the lower voltage side.

Perhaps. But technically, the primary is always the supply side, or whichever side is considered the supply side when interconnected systems are involved. If we get to the point where neither side is considered the supply side, then we do not have a primary/secondary scenario to begin with. :angel:

 

[big john]

That depends on what you call the primary/secondary. Some folks call the higher voltage side of the transformer the primary irrespective of the direction of current flow. Larger conductors are typically (always?) on the lower voltage side.

I was just talking about common scenarios, not certainties. Sometimes trannys are step-up in which case, I agree, primaries would be the low side, but I'd wager that's only true about 0.2% of the time.

 

[Carultch]

That depends on what you call the primary/secondary. Some folks call the higher voltage side of the transformer the primary irrespective of the direction of current flow.

I am not aware of any formal definition of how to know which side is primary and which side is secondary, in all applications. A physics book will tell you that the source of energy is on the primary side. And in most applications under the scope of the NEC, that is also the side toward the utility and also the side that is at higher voltage.

However, in the case of backfed transformers, it is a little less clear. Consider a PV application where a 208V to 480V transformer is used, with the inverters on the 480V side and the building is on the 208V side. Which side is primary? Which side should be governed by the NEC rules for "transformer secondary conductors"? I could take a poll of all of you, and I'd get half of the answers opposite the other half.

Larger conductors are typically (always?) on the lower voltage side.

That usually is precisely the reason why the transformers are used in the first place. To reduce the wire for long distance circuits. Voltage you pay for with plastic, current you pay for with metal.

Specifically, the conductive part of the larger conductors is larger. It very well may be that the wires with the larger overall OD are on the higher voltage side, because of the medium voltage insulation.

One counterexample is if the minimum medium voltage cable size per the utility standards is 1/0. If you are using it for 100A on the secondary low voltage side, you might have #2 on the secondary and #1/0 on the primary.