So I just want to get a bit of feedback and make sure I am not being silly here.

 

I have 2x inverters and to start with I will have 2x batteries, I want to connect the batteries to busbars and then from the busbars to the inverters - this will also make it easier if I want to add more batteries down the line as I then just connect those batteries to the busbars.

 

Based on this setup, my understanding / thinking is that there needs to be a fuse between the batteries and busbars and then again a fuse between the busbars and inverters?

I have always been taught and told that we run fuses to protect the cables and not the equipment - although this stems from car audio and the equipment generally has built in fuses already.

 

Below is a messy diagram I did in paint quickly to get my point across. I will ensure cable length are all equal at each part regardless of the route they take as I know that can cause some issues.

 

My thinking is that if there were to be something which happens between the busbars and batteries those fuses will blow, where if there is something which happens between the busbar and inverters then those fuses blow. The fuses between the batteries and busbar also allow for one to disconnect a specific battery from the busbar and the fuses between the busbar and inverters allow for one to easily disconnect the inverter from the batteries.

 

I do not think I can safely get away with using less than 4 sets of fuses in this current setup?

17 minutes ago, PsyCLown said:

I have always been taught and told that we run fuses to protect the cables and not the equipment - although this stems from car audio and the equipment generally has built in fuses already.

An electrician told me this once. In fact the fuses aren't even there to protect people (that's EL's job). If your cable can take 15A before it starts overheating then you should protect it with a fuse of less than 15A. I remember when we moved into our current home he found something like 10A cable with 15A fuses - fire risk!

The equipment will draw the power it needs, and if it needs protection then it should have it's own fuses or some other means of turning off or disconnecting. The fuses in the DB protect the wiring.

3 hours ago, Bobster. said:

An electrician told me this once. In fact the fuses aren't even there to protect people (that's EL's job). If your cable can take 15A before it starts overheating then you should protect it with a fuse of less than 15A. I remember when we moved into our current home he found something like 10A cable with 15A fuses - fire risk!

The equipment will draw the power it needs, and if it needs protection then it should have it's own fuses or some other means of turning off or disconnecting. The fuses in the DB protect the wiring.

There will always be diverse views on this topic. 

Take an example of a garden flat that is supplied with say a 4mm cable good for 30A. My tenant agrees to never use more than 1000W as we share the inverter during LS. I might use a 5A fuse to limit the flats use of power with a bit of grace. The inverter might have it's own say 13A thermal device being a 24V 3kW Axpert type inverter. 

Here the fuse performs it's main duty of limiting the current to the level chosen. 

Another exame I have a 70mm cable fitted between battery and inverter. I use a 0.5C battery good for 50A. I will use a fuse of say 75A although for a 70mm cable the cable protection fuse would be about 180A. This is where there is no setting on the inverter to set the maximum charge/discharge current. I would rather have the fuse blow than damage the battery. The battery's own overcurrent protection might be set at the 10sec discharge level. 

Thus the choice of fuse becomes application and design of system specific. 

Even overhead power lines have the current set to trip the line not at the level of the conductor size as thick conductors are used a lot of times to reduce voltage drop. The current is just one of the metrics used to decide on what is applicable. Some lines run say from De Aar all the way to the outskirts of Cape Town. Volt drop is a major problem. The whole network would be graded as far as the current setting is concerned. 

12 hours ago, Scorp007 said:

There will always be diverse views on this topic. 

Take an example of a garden flat that is supplied with say a 4mm cable good for 30A. My tenant agrees to never use more than 1000W as we share the inverter during LS. I might use a 5A fuse to limit the flats use of power with a bit of grace. The inverter might have it's own say 13A thermal device being a 24V 3kW Axpert type inverter. 

Here the fuse performs it's main duty of limiting the current to the level chosen. 

Another exame I have a 70mm cable fitted between battery and inverter. I use a 0.5C battery good for 50A. I will use a fuse of say 75A although for a 70mm cable the cable protection fuse would be about 180A. This is where there is no setting on the inverter to set the maximum charge/discharge current. I would rather have the fuse blow than damage the battery. The battery's own overcurrent protection might be set at the 10sec discharge level. 

Thus the choice of fuse becomes application and design of system specific. 

Even overhead power lines have the current set to trip the line not at the level of the conductor size as thick conductors are used a lot of times to reduce voltage drop. The current is just one of the metrics used to decide on what is applicable. Some lines run say from De Aar all the way to the outskirts of Cape Town. Volt drop is a major problem. The whole network would be graded as far as the current setting is concerned. 

I agree with this, although one should not have a fuse with a rating greater than the current the cable can handle.

As long as the fuse is at least equal to or less than the current rating of the cable, all should be good in terms of safety.

13 hours ago, Scorp007 said:

Take an example of a garden flat that is supplied with say a 4mm cable good for 30A. My tenant agrees to never use more than 1000W as we share the inverter during LS. I might use a 5A fuse to limit the flats use of power with a bit of grace. The inverter might have it's own say 13A thermal device being a 24V 3kW Axpert type inverter. 

Yes. They can be used as a limiter.

3 hours ago, Bobster. said:

Yes. They can be used as a limiter.

Can be / exclusively used? 

11 minutes ago, Scorp007 said:

Can be / exclusively used? 

OK I concede. What is up for debate is the reason for limiting. Might be to protect wiring (my initial point), but it doesn't have to be.

3 hours ago, Bobster. said:

Yes. They can be used as a limiter.

I've had great success at a student hostel with the 4A version of these current limiting protective devices. Culprits get disconnected for 60s whenever the load exceeds 920W.

5 hours ago, PsyCLown said:

I agree with this, although one should not have a fuse with a rating greater than the current the cable can handle.

As long as the fuse is at least equal to or less than the current rating of the cable, all should be good in terms of safety.

Correct statement and to just add to it,  it is essential that cables between battery and inverter needs to be short as possible as the de-rating with longer cables is actually very real. I use these formula to determine cable size in mm².

Current/3 = Cable size in mm² up to 5 meters. For example: if the current is 200A, then the cable needs to be:  200/3 = 66mm² for 5 meters so closest cable size is 70mm².

Edited August 18, 20232 yr by TaliaB

1 hour ago, Kilowatt Power said:

I've had great success at a student hostel with the 4A version of these current limiting protective devices. Culprits get disconnected for 60s whenever the load exceeds 920W.

Thanks for the link to a nifty device which a few members asked how to limit low current. 

Then on the other extreme on HV systems where no fuses can be used oil filled/SF6 gas multi ratio CTs are used to measure the current and signals are sent to a breaker to trip. 

On a 550kV CT the portion above the steel structure is over 6m tall. 

 

Edited August 18, 20232 yr by Scorp007

Anyways, so is my original post correct? Are all the fuses I have put in the diagram the necessary amount or is there a way to reduce the number of fuses required?

11 minutes ago, PsyCLown said:

Anyways, so is my original post correct? Are all the fuses I have put in the diagram the necessary amount or is there a way to reduce the number of fuses required?

Sorry yes @PsyCLownwe hijacked your post with similar matters but did not comment on what you actualy asked. I would use 2 Disconnectors as close to battery terminals possible. No need for fuses between busbar and inverters. If there should be a short anywhere along the route the fuses will blow.So 4 fuses 2 on each battery pos and neg.

Edited August 18, 20232 yr by TaliaB
Spelling

On 2023/08/17 at 3:17 PM, PsyCLown said:

So I just want to get a bit of feedback and make sure I am not being silly here.

 

I have 2x inverters and to start with I will have 2x batteries, I want to connect the batteries to busbars and then from the busbars to the inverters - this will also make it easier if I want to add more batteries down the line as I then just connect those batteries to the busbars.

 

Based on this setup, my understanding / thinking is that there needs to be a fuse between the batteries and busbars and then again a fuse between the busbars and inverters?

I have always been taught and told that we run fuses to protect the cables and not the equipment - although this stems from car audio and the equipment generally has built in fuses already.

 

Below is a messy diagram I did in paint quickly to get my point across. I will ensure cable length are all equal at each part regardless of the route they take as I know that can cause some issues.

 

My thinking is that if there were to be something which happens between the busbars and batteries those fuses will blow, where if there is something which happens between the busbar and inverters then those fuses blow. The fuses between the batteries and busbar also allow for one to disconnect a specific battery from the busbar and the fuses between the busbar and inverters allow for one to easily disconnect the inverter from the batteries.

 

I do not think I can safely get away with using less than 4 sets of fuses in this current setup?

This is the way my system was installed. And yes, 4 will be the minimum number of fuses in this scenario. You'll add another fuse block for every item you add, eg. an extra battery will bring the total to 5 fuse blocks.