Samlex EVO Grounding?

[JAS]

Hi everyone,

I've attached the wiring diagram for my Samlex EVO 4248. The Samlex manual recommends (and implies) that the grounding lug on the chassis is for the DC side and needs to be grounded to earth separately from the AC side.

However, looking at the schematic, the grounding lug and both AC grounds are all connected to the chassis. In addition, they are all eventually grounded to the same grounding rod. So why does it matter if the chassis lug has a ground connected or not?

And secondarily... why does Samlex also recommend connecting the battery negative to the same ground as well? I don't see anyone here doing that for off-grid systems...

EVO Manual for reference

 

[Dynoman]

Hi everyone,

I've attached the wiring diagram for my Samlex EVO 4248. The Samlex manual recommends (and implies) that the grounding lug on the chassis is for the DC side and needs to be grounded to earth separately from the AC side.

However, looking at the schematic, the grounding lug and both AC grounds are all connected to the chassis. In addition, they are all eventually grounded to the same grounding rod. So why does it matter if the chassis lug has a ground connected or not?

And secondarily... why does Samlex also recommend connecting the battery negative to the same ground as well? I don't see anyone here doing that for off-grid systems...

EVO Manual for refe

Running a Samlex EVO 2224 connected to the grid (transfer switches for backup 120VAC grid power when battery low) and the battery is not grounded or the chassis of the inverter connected to the DC (battery). The Samlex EVO 2224 is only grounded from the grid AC power input from the earth ground rod.
The Samlex EVO 2224 is supplying 120VAC to a critical load box and works well with no real problems for 3 years. Only minor issue is 3 times the cooling fan stuck on and had to power cycle the EVO.

My understanding the battery is connected to ground (chassis or frame of vehicle) in a mobile install not grid although some may disagree.

The Samlex EVO 4248SP is on my short list of inverter/chargers when making the move to 120/240 VAC. How Is the Samlex EVO 4248SP working out for you?

 

[JAS]

How Is the Samlex EVO 4248SP working out for you?

It's a beast! I tested it running my deep well pump (over 500' deep) and it didn't blink. It is a little funky with charging LifePO4 (especially when the batteries are new and the cells aren't balanced well). Basically, it freaks out when the BMS prevents charging (either due to cell overvoltage or low temp). I ended up using a chargeverter instead of relying on the built in charger of the EVO.

I originally had it hooked the same way with AC-In from the grid and didn't worry about any other grounds. Now, I'm changing things up and want to completely eliminate the AC-In. Hence, the confusion about what grounds are necessary...

 

[Backyard]

If the panel you are powering is already grounded, then don't add a second ground to the EVO. Just connect the EVO group to the panel ground.

If you are using it as a stand alone and no other earth ground exists, then, yes. Use the EVO chassis ground to earth it

 

[JAS]

If the panel you are powering is already grounded, then don't add a second ground to the EVO. Just connect the EVO group to the panel ground.

If you are using it as a stand alone and no other earth ground exists, then, yes. Use the EVO chassis ground to earth it

Thanks, that's what I was thinking too.

However, the ground for the AC Out is only 10awg. But, the chassis lug (which Samlex states is for "DC Grounding" accommodates a 4-6 awg wire...

 

[Backyard]

Thanks, that's what I was thinking too.

However, the ground for the AC Out is only 10awg. But, the chassis lug (which Samlex states is for "DC Grounding" accommodates a 4-6 awg wire...

Ground gauges are only such as to trip the OCPD. On the EVO, 10 AWG should be more then sufficient.

 

[JAS]

OCPD

So where is that in relation to grounding the inverter chassis? Is it the breaker on the AC Out side? Is it the fuse/breaker at the battery? I believe there is a fuse inside the EVO as well. Is that the OCPD? Or all of the above?

 

[JAS]

Oh... just read this in the Samlex manual.... Now I'm even more unsure

3.13 DC SIDE GROUNDING
Please refer to Fig 3.13.
DC side grounding involves bonding of the metal frame/chassis of EVO™, the metal chassis of the DC Electrical Panel
and the Battery Negative Terminal to Earth Ground in shore based installation (Fig 3.13). This ensures that in case of
a ground fault in the +48V circuit, the fuse in the +Battery line blows to clear the fault. This fuse in the +Battery line
has Ampere capacity matching the rated DC input current of the EVO™ in Inverter Mode. The wire size used for DC
side grounding should be minimum AWG #6 or of the same size as the battery cable, whichever is thicker (Battery
cable size should have minimum Ampacity ≥ the Ampere rating of this battery fuse depending upon the model of the
EVO™ being used). This recommendation on sizing of the DC Side Grounding Wire will be superseded by the
National / Local Electrical Codes.
i
INFO
As described at Section 3.14, the metal frame / chassis of the EVO™ (Fig 3.13) is bonded to the Grounding
Electrode "GE" (Ground Rod) for AC side grounding. It may be argued that if the metal frame / chassis of
EVO™ is already bonded to the Grounding Electrode "GE" for AC side grounding, why is it necessary to provide
additional DC side grounding wiring? (Wiring that bonds DC Grounding Terminals "5", "G-B" and GE in Fig
3.13). If separate thicker grounding wire of the same size as the battery cable was not provided for the DC side
grounding and there was a ground fault in the battery circuit, very large DC fault current from Battery+ would
flow through the smaller size AC grounding wires to the Battery Negative through Earth Ground. These smaller
size AC side grounding wires would be damaged due to very high DC side fault current (few hundred Amperes).


It does appear that this last paragraph refers to an issue where the battery negative is also grounded to earth. So if that is not the case, is there still a concern?

Oh... and is that only an issue for Lead Acid? IE: Shouldn't the BMS in a LifePO4 battery trip if there is a "very large DC fault current". For that matter, won't the fuse/breaker at the battery prevent that as well?

 

[JAS]

Here's the reply I got from Samlex Support... Doesn't leave things much clearer for me:

Hi Jeff,



Thank you for reaching out to us. The chassis lug denoted the DC side grounding, this grounds the chassis to the earth ground and once the negative terminal of the battery is grounded as well or connected to the earth ground it creates that connection. In the case of a ground fault, this allows the fuse in the +Battery line blows to clear the fault.



Connecting the grounding lug to the ground directly instead of relying in the grounding via the AC input ground allows for a shorter trouble between the inverter to the ground also since the Inverter is an Electrical Source. This is the same for Battery as it is an electrical source which is why the negative terminal of the battery is connected to the ground.



In the case you are wondering if your installation is properly grounded, you can reach out to your local Electrician and they will give you a better idea, as we can recommend grounding as based from NEC regulations.



Some more information on grounding can be found on page 53 and 55 of the manual.



Kind regards,


@FilterGuy What are your thoughts?

 

[FilterGuy]

@FilterGuy What are your thoughts?

Grounding one side of the battery used to be very common, particularly when the DC was galvanically isolated from the AC.
These days the inverter vendors don't talk about it and most people don't do it.

The Samlex design is clearly recommending grounding one side of the battery.... so I would do it.

Connecting the grounding lug to the ground directly instead of relying in the grounding via the AC input ground allows for a shorter trouble between the inverter to the ground also since the Inverter is an Electrical Source. This is the same for Battery as it is an electrical source which is why the negative terminal of the battery is connected to the ground.

What they are basicly saying is that by tying the ground lug to the grounding system, it creates a more direct path than through the AC ports. (The ground of the inverter AC ports are also connected to the Chassie)

 

[FilterGuy]

What they are basicly saying is that by tying the ground lug to the grounding system, it creates a more direct path than through the AC ports. (The ground of the inverter AC ports are also connected to the Chassie)

One thing that is unfortunate about this method is that it is likely to create a loop in the grounding circuits. This loop does not create a safety issue, but a ground loop with an inverter has a reasonably good chance of creating radio frequency noise.

 

[JAS]

The Samlex design is clearly recommending grounding one side of the battery.... so I would do it.

And here's the catch 22... EG4 has a big warning in their battery documentation to NOT ground the negative (or the positive for that matter)

I questioned Samlex support about grounding the battery and that I don't see anyone doing that in a stationary environment. (I've even seen @timselectric say NOT to do it) Here's their answer:

Hi Jeff,

That is interesting then, have not heard of people against grounding the negative, some off site server locations even have their positive line of the battery grounded instead of the negative line due to select cases. As comparison in vehicles, the negative of the starter battery is always connected to the chassis of the vehicle, while in a Marine vessel, the negative terminal is required to be grounded with a gauge 1 size smaller than the DC wiring. These are all comparisons on other usual installations other than an Off-grid cabin.

Do note that grounding the unit is required by National / Local Electrical Codes / Standards thus it is the responsibility of the user / system installer, whether it is AC Grounding or DC Grounding. That is all where it comes down too.

So it seems to me that Samlex is not at all familiar with environments outside of the mobile and marine markets...

I'm pretty sure I will not be grounding the battery. (If for no other reason than to not void my EG4 battery warranty). However, does anyone see any harm in adding a 6awg ground wire to the inverter lug in addition to the existing AC-Out ground?

 

[Dynoman]

However, does anyone see any harm in adding a 6awg ground wire to the inverter lug in addition to the existing AC-Out ground?

If I understand the question and am looking at the schematic properly of the Samlex EVO 4248SP...

It appears that there would be nothing gained in grounding to the inverter case ground lug (DC side grounding terminal listed 5 in schematic) and the (G VAC output terminal in schematic). Both the (G VAC output terminal ground) and (DC side grounding terminal 5) go to the Samlex EVO 4248SP metal chassis.

It appears the (G VAC output terminal ground) on the Samlex EVO 4248SP connected to the earth ground rod would be sufficient.

Certainly not a ground loop expert, but 2 different wires with different resistance to the same chassis may cause problems?


That's my 2 cents...

 

[Backyard]

If I understand the question and am looking at the schematic properly of the Samlex EVO 4248SP...

It appears that there would be nothing gained in grounding to the inverter case ground lug (DC side grounding terminal listed 5 in schematic) and the (G VAC output terminal in schematic). Both the (G VAC output terminal ground) and (DC side grounding terminal 5) go to the Samlex EVO 4248SP metal chassis.

It appears the (G VAC output terminal ground) on the Samlex EVO 4248SP connected to the earth ground rod would be sufficient.

Certainly not a ground loop expert, but 2 different wires with different resistance to the same chassis may cause problems?


That's my 2 cents...

Ground loop would be my only concern. This is really only an issue if the ground points are further away. Like one ground rod for the main panel and a second at the inverter. Then, as you pointed out, different resistance between them and the wires can create a ground loop where current can continuously flow through them creating issues.

Grounding the chassis would depend on what the systems grounding looks like. If there is no earth ground anywhere else in the system then chassis ground earthing would be a good idea. If there is already one at the panel then don't add a second one

 

[JAS]

Thanks guys!

I've decided to just leave as is with the AC-Out ground connected to earth ground (via the panel it is feeding)