samlex

rich

Hello All, I havnt logged in for a while, started writing this in BC but am now in Ab,it was longer then but edited it down before pasting and posting..lol my journey has been allot of fun and after allot of experimentation ended up with two kid controllers(on back order) a chinese inverter charger w-7 type,an Iota 24 volt charger 1400 watts in 100watt panels and a samlex proper sine 1000 watt inverter, ..Here is my problem...my system is a floating ground , fused on all positive and negative lines including inline fuses(mc4 type) on both pos and neg pv input, the only ground (NOT CONNECTED YET)will be from my battery neg. to my trailer chassis...i also have a lightning surge for incoming pv....sounds like overkill?, not sure?

ok The ground fault breaker on my samlex inverter trips ,it usually happens about 6 to ten hours after I plug it in..it is only used to run my bar fridge which was barely running off a 800 watt chinese inverter, it got so hot the blade fuses melted and dripped the plastic right off the fuse element, the it failed...so I replaced it with the samlex and have a ground fault issue...is there a way to defeat the ground fault recepticle?..this is my ultimate goal here....any ideas?

Cariboocoot

Re: samlex

Let's try to narrow this down a bit. You have a Samlex inverter; which model?
It has built-in receptacle with GFCI. The refrigerator trips the GFCI after about ten hours. The only thing grounded is the battery negative?

Well if the battery negative is actually connected to Earth ground then your double fusing is redundant. Double fuses, btw, don't work for floating systems; it needs to be breakers that trip off both positive and negative at the same time regardless of which one develops a problem. Usually it is unnecessary even without ground.

Your inverter is supposed to be grounded in order for the GFCI to work properly. It's checking for current match between Hot and Neutral. Neutral is bonded to ground before the GFCI circuit so if the Hot shorts to ground after it a current imbalance is created between Hot and Neutral, GFCI trips, power shuts down. If something in the refrigerator is causing a connection to ground from hot the GFCI should trip. If the inverter is not grounded then there is not zero Voltage potential between Neutral and ground and the GFCI can false trip. That said, GFCI's are notorious for false trips anyway.

As long as you don't care about warranty and feel comfortable doing so you can open up the inverter and remove the GFCI outlet then replace it with a standard one (pretty sure the GFCI is in the receptacle on those, but some have the circuitry on the board). It won't be the first time this has been done.

rich

Re: samlex

Hi , thanks for the quick retort, as far as the fuses in each panel string it cant hurt so until the kid controllers arrive they are a cant hurt anything issue, I havnt grounded my bank to the chassis yet as IM very parinoid of near strikes ,I have had several in my time..MR Coot , are You saying that my ground fault issue will go away if I make the final ground connection between my bank and chassis?, I have all my dc applications fused on the neg side and the posative, not breakers, this includes,inverters , and also between the c/cs and battery...i use a switching power supply to step to 12 v from 120v for my audio system and cb radio and phone chargers /so-on.these circuits are 12 volt and stand alone breakers similar to marine..as far as ac. I havnt made the neutral ground connection yet in my ac panel box...when my w-7-inverter is connected to grid it has a transfer switch that ties its neutral to ground using the grid supply, it disconnects that tie when in ups inverter mode.but I havnt tied the individual circuits to that bus yet..there is a bus bar for this in my panel box, should I do it?..i was hoping my lightning arrester would be already here first, Am I bieng ureasonable to operate my equipment like this? ..my inverter is samlex sa 1000k 24 volt version.........I guess redundancy is my querk, im a two is one kinda fella...can it hurt to have the fuse protection like this or do I 'need to have breakers to insure my wire is protected( I have oversized all my wires to help this matter,) I just dont get it , its like I have a primal fear of connecting these grounds to neutral yet I feel it a must to chassis ground...I have tested the fridge and I cannot detcct any short to to the chassis and with individual circuits when breaker is open with nothing plugged in i get no continuity beep on my meter, sooo, do You think connecting that dc to chassis will help with the dc ac inverter and tripping the gfci?...I would not want to void any warrenties on this type of equipment.....thanks ..

Cariboocoot

Re: samlex

I'm only saying having a real ground connection for the inverter may cure the GFCI problem. Frankly those things are trouble no matter who makes them and where they are installed. I had one burn up on a household circuit with nothing connected to it. Yeah, fun.

It sounds like you may be asking for trouble with the N-G issue. That Samlex inverter has such a bond built-in, and you don't want another anywhere in your AC wiring when the inverter is connected to it.

The redundant fuses on the negative wiring won't hurt anything, they just won't help: current is the same throughout the circuit and therefor needs only one 'weak spot' to trip if something goes wrong. The reason dual ganged breakers are used in such applications is the same as with 240 VAC wiring: if something shorts either side both sides are shut off. Without that trip connection between the two (which fuses obviously can't have) the additional OCP doesn't really help.

vtmaps

Re: samlex

Cariboocoot wrote: »

Double fuses, btw, don't work for floating systems; it needs to be breakers that trip off both positive and negative at the same time regardless of which one develops a problem.

I don't follow this logic... I thought the purpose of the fuses is to protect the wiring. If every wire is fused appropriately, then every wire is protected.

From a very recent thread:

BB. wrote: »

Another reason to ground your battery bank... If you get a short circuit somewhere between + and chassis somewhere (cable is cut/worn and contacts chassis), the short circuit will pop a fuse or circuit breaker.

If you have a floating battery power system--Then the "first short" sets the system grounding (i.e., a - short to ground makes negative ground; a + to ground short makes a positive ground)--Then the second short causes the current to flow. And at that point, you don't know where and how much current will flow. Say that your 2 awg AC inverter + wire makes the first short. And the second short is a - 14 AWG wire from a DC lighting fixture--In a "normal" system, you only have fuses in the + leads--So you have your 200 amp fuse in the plus lead and no fuse in the 14 AWG return lead--And your 14 AWG wire gets red hot and causes a fire.

So--For floating power systems, to be safe, you need a fuse/breaker in both the + and - wire runs--2x more protective devices.

--vtMaps

Cariboocoot

Re: samlex

vtmaps wrote: »

I don't follow this logic... I thought the purpose of the fuses is to protect the wiring. If every wire is fused appropriately, then every wire is protected.

From a very recent thread:


--vtMaps

Because two fuses on the same circuit won't blow at the same time, so there is no point in having two fusses.
Ganged breaker trips from either side, disconnects both power lines.

vtmaps

Re: samlex

Cariboocoot wrote: »

Because two fuses on the same circuit won't blow at the same time, so there is no point in having two fusses.
Ganged breaker trips from either side, disconnects both power lines.

Are you saying Bill's explanation of why fuses are needed on both pos and neg wires (in a floating ground system) is wrong, or am I misunderstanding his logic?

--vtMaps

Cariboocoot

Re: samlex

vtmaps wrote: »

Are you saying Bill's explanation of why fuses are needed on both pos and neg wires (in a floating ground system) is wrong, or am I misunderstanding his logic?

--vtMaps

Well I don't understand why he thinks this would help. Probably he just didn't write what he meant, which often happens when switching contexts.

BB.

Re: samlex

In the old days, you can use two fuses (or independent breakers) to at least one leg of a floating output.

If you follow NEC code--For something like 120/240 VAC Split phase power (common grounded neutral), they want a "ganged" breaker so that both legs are turned off at the same time to prevent somebody assuming that a circuit is dead when only one of the "hots" has opened.

The problem with floating power circuits--The first "short" does not conduct any current--So there is no "over current hazard" is created.

The problem is the "second short" circuit. This now causes power to flow through the system, and in my example, you could have high current flow start at a +200 amp bus and return through a -15 amp return wire.

If you only had fuses in the + line and a floating system--You could easily burn out the 15 amp return wire (typically a minimum of ~14 AWG wire).

So--You are forced (for safety) to fuse leads that leave both the + and - Buses. I have not seen any common fuses/DC Breakers that are ganged for, what I would suggest, is a "safe" disconnect for a floating power system (break mated +/- wire sets) at the same time (for "shock safety").

We are then left with using individual fuses/breakers in a floating system so it will be "safe"(er) from a over current wiring point of view... But not safe from a break both +/- connections to "kill" all power to a branch circuit (because both +/- fuses do not interrupt both sides of the circuit if one fuse pops).

With "real" engineered floating circuits--They will either have a test setup (for example, tested once a day/week to make sure the system is truly floating... Or they have a circuit that monitors in real time if the circuit is floating. And with AC, we have cheap/reliable/available ganged breakers available to cut both side of a floating (or Hot/Neutral/Hot or even 3 phase) circuit.

Anyway--That is why is is usually easier to put a grounded return (typically negative for battery systems, and ground bonded neutrals for North American AC systems)... It gets rid of a whole bunch of other issues.

In the end--What is normally done?. Typically for floating systems (say portable battery power)--You will typically only find one fuse in the + lead.

I would suggest that for permanently installed DC power systems, that the return is always bonded to frame/vehicle/cabin ground (solves Single/Double fuse question, prevents static build up issues, and can help reduce the chance of lightning damage).

For permanently installed AC systems... If it is MSW (Modified Square/Sine wave) inverter--You generally cannot safely ground bond the "neutral". So don't do it (DC ground and AC neutral bonding to ground creates a short circuit through most MSW inverters).

For permanently installed AC system... If it is a TSW (True Sine Wave) inverter--You generally can safely ground bond both the DC and AC Neutral side without issues. For smaller TSW AC power systems (say less than 1,500 Watts)--Ground bonding of the neutral is up to you. Normally 14 AWG wire is the minimum size or ~15 amps current flow rating--And a 1,500 Watt 120 VAC inverter cannot exceed the rated current anywhere in the AC power system--So a single fuse is "OK" in a floating power output.

For RV's that connect to shore power, have an AC inverter, and an AC Genset--Same issues, but more discussion to make sure it is safe in all operating configurations.

As always, read the manuals for the AC inverters--There are some out there that are "different" (i.e., electrically isolated MSW AC output which could be ground referenced neutral) or TSW inverters that already have a ground bonded AC neutral connected inside.

-Bill