Transfer switch priority

[Brian B-P]

Originally Posted by M_canada

The reference I found was from the older T-30 user manual (https://wfcoelectronics.com/wp-conte...57R-Manual.pdf). In one section it sort of implies generator priority:
“Shore Power to Generator Power Transfer Time Delay
Time delay (30 sec. nominal) allows gensets to complete self-diagnostics before power is transferred”

That's in the current manual, but I don't think this statement implies generator priority (although your test has confirmed generator/inverter priority). Even if there is no power source functioning to start (so the switch is in shore power mode because that's the no-input default) and the generator input comes on, it will wait for this time delay to let the "generator" stabilize; that is unrelated to how the transfer switch chooses what source to use when both are available.

Of course this delay is unnecessary and excessive with an inverter, but as already discussed these transfer switches are designed for generators. Maybe there's something to be said for the inverters with integrated transfer switches, although they usually seem to be limited more in current capacity than desired.

[scubarx]

Originally Posted by Brian B-P

...it's not often (if ever) that anyone wires separate inputs to the outside of an RV, with one for shore power and the other for generator power...

Both of our Oliver's have been wired like that, but each input passes through a Progressive Dynamics Series 5100 30-Amp Automatic Transfer Switch before connecting to the AC Distribution Panel.

[Jim Bennett]

Originally Posted by M_canada

I haven't wired up a remote on/off for the inverter, but maybe I should do that.

I did this when I installed the inverter in my trailer. Placing it above the fridge where a couple other panels are is a great place to have it, and easy to shut off when not in use.

[RangerMan]

Never occurred to me that the ETI installed xfer switch was designed for a generator and had the inputs so labeled.

I know without a doubt that my xfer switch is shore power dominate but I'm going to check for any input labels next time I use it just out of curiosity.

[Brian B-P]

Originally Posted by scubarx

Both of our Oliver's have been wired like that, but each input passes through a Progressive Dynamics Series 5100 30-Amp Automatic Transfer Switch before connecting to the AC Distribution Panel.

You have two power inlets on the outside of the trailer, one for shore power and one for an external generator which is not mounted on the trailer? That's strange, but of course it would work for that rare situation in which you need to switch between shore power and generator power without changing which cable is plugged in. It seems like an unnecessary transfer switch.

If the generator is mounted on the trailer, then it's just an onboard power source, like any other onboard generator or inverter. That's what these transfer switches are designed for.

[Brian B-P]

Originally Posted by oldwave

Ah I ve read about those hybrid inverters that augment the load of a small generator to help start an ac that has a large capacitor load upon initial power. Is that what this mode is for ?

Those "hybrid" systems are slick, but I don't think that's what Marc (M_canada) is describing. The ECO feature shuts the inverter off, even when it is enabled and there is no shore power, to avoid idle power consumption. When a load (such as an appliance) is turned on nothing happens initially (because there is no power), but when the inverter blips the power on for a moment (because it is in ECO standby mode) some current flows and that's the signal to "wake up" the inverter to start operating normally. When all loads are turned off, output power from the inverter goes to zero, and the inverter goes back to "sleeping" in ECO standby mode, just blipping the power on occasionally to see if it is needed. Right, Marc?

[Brian B-P]

Originally Posted by M_canada

It has also reminded me other another drawback to the transfer switch having shore power designated as the ‘pass through’ input. My inverter has an ECO mode where it periodically turns on the AC output and checks for a minimum AC load. This can reduce idle power draw to less than 3W. The transfer switch needs the generator input to be active for 30 seconds and operates the relay to switch to the generator input, so ECO mode doesn’t work. I think if I swap the input connections at the transfer switch, I will be able to use the ECO mode and solve most of my issues.

I think it's important to separate three distinct features of the transfer switch:

Shore Power Pass Through

This is what determines how the transfer switch makes connections when there is no power source, and which connection doesn't need a relay to be energized. If this inverter is in ECO mode and there is shore power, then the transfer switch will connect whatever is on the pass-through terminals (which are designated "shore power"), so that should be the inverter. This is true regardless of the other two features. Unfortunately, it means that if the trailer is stored with shore power connected to keep the battery maintained, and the shore power is connected to the "generator" input, then the transfer switch relays will be energized for the entire storage time.

Generator Priority

This is what determines how the transfer switch makes connections when both power sources are active. This situation should never occur with a typical inverter such as the one supplied by Escape (unless you accidentally leave the inverter on when it should be turned off). If you make use of this inverter's ECO mode to just leave the inverter on all of the time, then the shore power should have priority instead... but you don't need to do that, you can just turn the inverter off when on shore power.

Shore Power to Generator Power Transfer Time Delay

This delay occurs on switching the input designated as "generator" on, regardless of why it is going on. It is only intended for generators, is unnecessary for inverters, is at least a minor annoyance, and should ideally be disabled or adjusted to minimum time if possible. It is incompatible with the ECO mode, since the inverter's checking blip wouldn't last long enough to trigger the switch to the inverter.

So the features are not related, but all would work better for this inverter's ECO mode if the inverter were fed to the "shore power" designated input and the shore power to the "generator" designated input, as proposed.

[M_canada]

Originally Posted by Brian B-P

I think it's important to separate three distinct features of the transfer switch:

Shore Power Pass Through

This is what determines how the transfer switch makes connections when there is no power source, and which connection doesn't need a relay to be energized. If this inverter is in ECO mode and there is shore power, then the transfer switch will connect whatever is on the pass-through terminals (which are designated "shore power"), so that should be the inverter. This is true regardless of the other two features. Unfortunately, it means that if the trailer is stored with shore power connected to keep the battery maintained, and the shore power is connected to the "generator" input, then the transfer switch relays will be energized for the entire storage time.

Generator Priority

This is what determines how the transfer switch makes connections when both power sources are active. This situation should never occur with a typical inverter such as the one supplied by Escape (unless you accidentally leave the inverter on when it should be turned off). If you make use of this inverter's ECO mode to just leave the inverter on all of the time, then the shore power should have priority instead... but you don't need to do that, you can just turn the inverter off when on shore power.

Shore Power to Generator Power Transfer Time Delay

This delay occurs on switching the input designated as "generator" on, regardless of why it is going on. It is only intended for generators, is unnecessary for inverters, is at least a minor annoyance, and should ideally be disabled or adjusted to minimum time if possible. It is incompatible with the ECO mode, since the inverter's checking blip wouldn't last long enough to trigger the switch to the inverter.

So the features are not related, but all would work better for this inverter's ECO mode if the inverter were fed to the "shore power" designated input and the shore power to the "generator" designated input, as proposed.

Excellent summary, thanks!

I swapped the connections so that the external AC shore power input is connected to the transfer switch input labeled 'generator' and the the inverter AC output is connected to the transfer switch 'shore' input. It now works exactly as I would prefer for my application. My inverter ECO mode works perfectly now and the relay is not energized when running from the inverter. I'm going to connect with WFCO on Monday to try and get their blessing for using it this way.

I also took a few photos of the original transfer switch wiring and the label on the back. From the wiring, you can see the black inverter power cord connected to the 'generator' input of the transfer switch, so it is wired as per the manufacturer. You can also see the label indicates there is an internal switch to bypass the delay, but I didn't open it up to verify. Also interesting is that the schematic shows both shore power and generator power inputs are internally wired through normally open (NO) inputs. I was expecting to see a normally closed shore power input and a normally open generator input.

[Centex]

I don't think I've seen this mentioned in the thread up to now, my apology If I missed it ...

When considering which TS (Transfer Switch) inputs to use for which power source IMO it's important to understand how the TS addresses the neutral>ground bonding situation. Many TS's toggle between a 'bonded' and 'un-bonded' condition depending on the input selected, and that can bear on safety of the electrical system in case of certain types of wiring or connected device faults.

While some EMS-type devices will detect and warn or protect from faulty neutral/ground bonding situations occurring in the circuit before the EMS, AFAIK they will not provide similar protection from such faults occurring after the EMS in the circuit. AFAIK most EMS installations are located before the TS, offering no warning or protection from such faults occurring within or after the TS.

The point being IMO a thorough understanding of these neutral/ground bonding implications and how/where bonding occurs in your specific system of AC distribution for each source-selection is in order before randomly swapping the default input sources at a TS.

Just for your consideration.

[RangerMan]

Originally Posted by Brian B-P

Those "hybrid" systems are slick, but I don't think that's what Marc (M_canada) is describing. The ECO feature shuts the inverter off, even when it is enabled and there is no shore power, to avoid idle power consumption. When a load (such as an appliance) is turned on nothing happens initially (because there is no power), but when the inverter blips the power on for a moment (because it is in ECO standby mode) some current flows and that's the signal to "wake up" the inverter to start operating normally. When all loads are turned off, output power from the inverter goes to zero, and the inverter goes back to "sleeping" in ECO standby mode, just blipping the power on occasionally to see if it is needed. Right, Marc?

Seems a bit outdated to use the polling method (pick up the phone to see if anyone is there) rather then the interrupt method (The phone is ringing, answer it!) to determine if power is needed.

I would bet $2 that the system described uses the interrupt method. "Hey, I need some power here."

My Honda generator works that way. When it's in the 'eco' mode if it detects more power is needed, it ramps up to supply it.

[Brian B-P]

Originally Posted by M_canada

Also interesting is that the schematic shows both shore power and generator power inputs are internally wired through normally open (NO) inputs. I was expecting to see a normally closed shore power input and a normally open generator input.

That's what I would expect, too, and I suspect that's just an error in the drawing. The coil is clearly shown as powered by a circuit supplied by the "generator" input, which is consistent with the "shore power pass through" feature... which would be the case if the "shore power" contacts are normally closed. There are not two coils, to drive the contacts in two different directions from a non-connected middle state; there is only one coil to drive it from the unpowered state ("shore power" contacts closed) to the powered state ("generator" contacts closed)

I did a quick search and found a (lower current rating) relay from Tyco used for this purpose, and the datasheet confirms that one set of inputs are normally closed (connected to the commons). I don't know what specific relay is actually used by WFCO.

[M_canada]

Originally Posted by Centex

I don't think I've seen this mentioned in the thread up to now, my apology If I missed it ...

When considering which TS (Transfer Switch) inputs to use for which power source IMO it's important to understand how the TS addresses the neutral>ground bonding situation. Many TS's toggle between a 'bonded' and 'un-bonded' condition depending on the input selected, and that can bear on safety of the electrical system in case of certain types of wiring or connected device faults.

While some EMS-type devices will detect and warn or protect from faulty neutral/ground bonding situations occurring in the circuit before the EMS, AFAIK they will not provide similar protection from such faults occurring after the EMS in the circuit. AFAIK most EMS installations are located before the TS, offering no warning or protection from such faults occurring within or after the TS.

The point being IMO a thorough understanding of these neutral/ground bonding implications and how/where bonding occurs in your specific system of AC distribution for each source-selection is in order before randomly swapping the default input sources at a TS.

Just for your consideration.

Thanks for bringing this up. I had no neutral bond when I had the inverter connected to the generator input, so I should be ok. I don’t see any indication that this transfer switch bonds the generator neutral input to ground. I would expect huge warnings in the installation manual if it did that because I think that would be bad if your generator was bonded too. I’m a bit surprised that you have found transfer switches that do that. Do you know why they would do that instead of bonding back at the generator? I will be sure to double check with WFCO when I call them on Monday.

[Brian B-P]

Originally Posted by Centex

When considering which TS (Transfer Switch) inputs to use for which power source IMO it's important to understand how the TS addresses the neutral>ground bonding situation. Many TS's toggle between a 'bonded' and 'un-bonded' condition depending on the input selected, and that can bear on safety of the electrical system in case of certain types of wiring or connected device faults.
...
The point being IMO a thorough understanding of these neutral/ground bonding implications and how/where bonding occurs in your specific system of AC distribution for each source-selection is in order before randomly swapping the default input sources at a TS.

Just for your consideration.

Yes, the neutral is important. This transfer switch simply switches the neutral as well as the line (or "hot") wires; there is no neutral to ground bonding in the transfer switch, and there shouldn't be any such bonding anywhere else in the trailer.

[M_canada]

Originally Posted by Brian B-P

That's what I would expect, too, and I suspect that's just an error in the drawing. The coil is clearly shown as powered by a circuit supplied by the "generator" input, which is consistent with the "shore power pass through" feature... which would be the case if the "shore power" contacts are normally closed. There are not two coils, to drive the contacts in two different directions from a non-connected middle state; there is only one coil to drive it from the unpowered state ("shore power" contacts closed) to the powered state ("generator" contacts closed)

I did a quick search and found a (lower current rating) relay from Tyco used for this purpose, and the datasheet confirms that one set of inputs are normally closed (connected to the commons). I don't know what specific relay is actually used by WFCO.

Maybe I’ll open it up and check if I get bored...I can’t imagine it is a complicated circuit board.

[Brian B-P]

Originally Posted by M_canada

I’m a bit surprised that you have found transfer switches that do that. Do you know why they would do that instead of bonding back at the generator?

I can only guess that they consider they consider the transfer switch to be the equivalent to an entry panel in a building, the only point where the neutral and ground are bonded. It seems to me that to do this properly (bond them only for the generator input) the transfer switch would need to be a triple pole configuration, or the usual double-pole double-throw (for line and neutral) plus a single-pole single-throw for the bonding, operated in synch.

[Brian B-P]

Originally Posted by M_canada

Maybe I’ll open it up and check if I get bored...I can’t imagine it is a complicated circuit board.

It should be a single DPDT relay plus whatever does the delay and perhaps a minimum voltage check on the side which triggers switching (unless they're just depending on the relay coil's voltage requirement to engage).

In addition to a simple multimeter test of the contact states, if you dig far enough to see the actual relay, it may have a schematic printed on the case.

By the way, the simplicity of this system explains why it is generator-priority: to get the shore power pass through, the switching is controlled simply by the existence of voltage on the other input - regardless of what shore power is doing. So whenever there is power from the generator input, it switches to that: "generator priority".

[M_canada]

Originally Posted by RangerMan

Seems a bit outdated to use the polling method (pick up the phone to see if anyone is there) rather then the interrupt method (The phone is ringing, answer it!) to determine if power is needed.

I would bet $2 that the system described uses the interrupt method. "Hey, I need some power here."

My Honda generator works that way. When it's in the 'eco' mode if it detects more power is needed, it ramps up to supply it.

It has to power up the inverter output to 120 VAC and then check if the load current/wattage is over a configurable minimum. I’m not sure how you could reliably detect the load without turning on the output. I’ve attached the ECO search settings for the inverter. The data sheet for the inverter states:
“ ECO mode
When in ECO mode, the inverter will switch to standby when the load decreases below a preset value (min load: 15W). Once in standby the inverter will switch on for a short period (adjustable, default: every 2,5 seconds). If the load exceeds a preset level, the inverter will remain on.”

[Brian B-P]

Originally Posted by RangerMan

Seems a bit outdated to use the polling method (pick up the phone to see if anyone is there) rather then the interrupt method (The phone is ringing, answer it!) to determine if power is needed.

I would bet $2 that the system described uses the interrupt method. "Hey, I need some power here.".

The problem is that the load has no way to "ring the phone", which is why the inverter must regularly check.

Originally Posted by RangerMan

My Honda generator works that way. When it's in the 'eco' mode if it detects more power is needed, it ramps up to supply it.

The Honda generator is running in Eco mode, unlike the inverter with ECO mode - it doesn't need to query anything and doesn't receive any information; it just adjusts speed to maintain voltage, the way a car's cruise control adjusts power to maintain speed.

[rubicon327]

Originally Posted by Centex

When considering which TS (Transfer Switch) inputs to use for which power source IMO it's important to understand how the TS addresses the neutral>ground bonding situation. Many TS's toggle between a 'bonded' and 'un-bonded' condition depending on the input selected, and that can bear on safety of the electrical system in case of certain types of wiring or connected device faults.

Originally Posted by Brian B-P

Yes, the neutral is important. This transfer switch simply switches the neutral as well as the line (or "hot") wires; there is no neutral to ground bonding in the transfer switch, and there shouldn't be any such bonding anywhere else in the trailer.

Originally Posted by Brian B-P

I can only guess that they consider the transfer switch to be the equivalent to an entry panel in a building, the only point where the neutral and ground are bonded. It seems to me that to do this properly (bond them only for the generator input) the transfer switch would need to be a triple pole configuration, or the usual double-pole double-throw (for line and neutral) plus a single-pole single-throw for the bonding, operated in synch.

I believe these simple transfer switches like the WFCO T-30 assume you are using shore power or a generator with neutral bonded to ground at the power source only in either case. Since an inverter is being used as a power source shouldn’t that technically have a neutral-ground bond? I believe Centex (Alan) may be referring to more complex combination inverter/transfer switch units that bond when inverting and unbond when on shore power. For example the Xantrex Freedom XC that we are both installing do it. See attached. Not to open a can of worms here but the way these inverters are typically wired to these basic transfer switches probably doesn’t meet the NEC.

[RangerMan]

Originally Posted by M_canada

It has to power up the inverter output to 120 VAC and then check if the load current/wattage is over a configurable minimum. I’m not sure how you could reliably detect the load without turning on the output. I’ve attached the ECO search settings for the inverter. The data sheet for the inverter states:
“ ECO mode
When in ECO mode, the inverter will switch to standby when the load decreases below a preset value (min load: 15W). Once in standby the inverter will switch on for a short period (adjustable, default: every 2,5 seconds). If the load exceeds a preset level, the inverter will remain on.”

You should have taken my bet.😊