After quite a few days of research I've been doing on the topic in question, people all over suggest that Welding Cable can be used instead of Battery Cable for Solar systems; however, people tend to prefer Battery Cable as they believe it's cheaper than Welding Cable.

 

I however found with searching through many online stores that Welding Cable tends to be slightly cheaper (obviously depending on where you buy), but in general the pricing seems slightly better (based on the same size mm² vs mm² comparisons).

 

What I find interesting is the following comparisons ...

 

Battery Cables:

• Averages around 60V
• Fewer copper strands
• Low to moderate flexibility
• Not flame resistant

 

Welding Cables:

• Easily exceeds 400V+
• More copper strands
• Greater flexibility
• Flame resistant

The chart below is based on approved SABS 1574 standards and ratings:

 

However what can't seem to escape me is, the fact that for Welding Cable you'll use a way smaller size cable to do the same job when compared to Battery Cable, ie. 16mm² Welding Cable compares to 35mm² Battery Cable (technically between 25mm² and 35mm²).

 

My question is, why do you need 35mm² for 125A ~ 140A charge / discharge using Battery Cables when 16mm² Welding Cable can suffice?

* even if you choose to play it safe and rather obtain 25mm² Welding Cable you will still be way aboveboard when compared to Battery Cable (purely based on the amperage)

 

Is this purely a matter of personal preference or choice, or are there any sinister items I am overlooking: ie. degrading factors on Welding Cable with tin lugs vs Battery Cable or oxidation at greater heat or such?

 

Surely if there are no ill effects of using Welding Cable, then by assumption based on the above the following can safely be used?

1. 16mm² Welding Cable for a max continuous 100A charge / discharge
2. 35mm² Welding Cable for a max continuous 190A charge / discharge

 

Looking forward to the replies ... 🙂

Edited August 19, 20224 yr by RabidBunny

Most places will sell you welding cables for your batteries. Many installers use it. The mm² should not differ between the two, for welding you don't mind hotter cables, but for batteries the losses are the important thing - so stick to the battery recommendations for cable gauge.

The main difference between the two is the insulation. Welding cable has high temperature insulation, which allows for higher continuous conductor temperatures.

Either way, I believe you will be limited to the SANS-10142 limits for fixed installations, table 6.2 for PVC or 6.9 for high temperature cable (derated to 75% if enclosed).

So you can get away with slightly smaller welding cables, but not quite as small as the table you provided.

48 minutes ago, JustinSchoeman said:

So you can get away with slightly smaller welding cables, but not quite as small as the table you provided.

The Battery Cable amperage ratings provided, is from the actual manufacturers' website (for the exact cables in question).

The Welding Cable amperage ratings provided is also from the actual manufacturers' website, they attached alongside it the relevant approvals and certification from SABS, etc.

 

If you consider the 75% de-rating factor then it means in order to "safely" charge / discharge at 190A, (for these cables based on the above charts/ratings), then one would need the following:

Battery Cables @ 120mm² ~ Sunsynk recommends 50mm² and Deye recommends 35mm² (for 190A charge / discharge); however, to be honest I've never even seen an installation ("domestic") using this size cabling ... 50mm² or 70mm² sure

Welding Cables @ 50mm² ~ for 190A charge / discharge ... 50mm² seems reasonable

 

However many manufacturers have a degree of protection integrated, ie. from 5% upwards some even as high as 15%

OK, I see:

Quote

6.2.6.4 For the size and construction of a cable and for the conditions of
use, other than those covered in this clause and the following tables, the
current-carrying capacity shall be taken as that specified by the
manufacturer or as given in SANS 10198-4.

So, under some conditions you can use the cable manufacturer's specification.  But you do need to pay careful attention to the specification.  It is normally for an open air installation at a specific temperature and for a maximum time (which will be specified in the product datasheet, and not necessarily in an on-line product blurb).

You still need to apply the SANS-10142 deratings and voltage drop limits when selecting the cable.

1 hour ago, JustinSchoeman said:

OK, I see:

So, under some conditions you can use the cable manufacturer's specification.  But you do need to pay careful attention to the specification.  It is normally for an open air installation at a specific temperature and for a maximum time (which will be specified in the product datasheet, and not necessarily in an on-line product blurb).

You still need to apply the SANS-10142 deratings and voltage drop limits when selecting the cable.

Selecting a 35mm welding cable that is good for 220A at 100% duty cycle would be fine. Very few people have enough PV or battery storage to exceed the save limit for hours on end. This before derating. Welding cable temp can be up to 85 degrees vs 70 for normal PVC. Voltage drop should seldom be a problem due to the short cable length. At 1.5m between the battery and inverter is only about 0.5V. This is 20 times less than what SANS 10142 allows.

@RabidBunny

Interesting you mention SANS 1574 as well as 400V for welding cable. My specs indicate a maximum of 100V to earth.

Edited August 19, 20224 yr by Scorp007

1 hour ago, JustinSchoeman said:

So, under some conditions you can use the cable manufacturer's specification.

Yes, that's what I'm trying to confirm, thanks!

 

You clearly outlined it nicely in this quoted section:

Quote

6.2.6.4 For the size and construction of a cable and for the conditions of
use, other than those covered in this clause and the following tables, the
current-carrying capacity shall be taken as that specified by the
manufacturer or as given in SANS 10198-4.

What baffles me though, is that if you phone (almost any supplier), asking for the amperage rating for 35mm² Battery Cables, I can guarantee you almost every single one of them will tell you something different and at the end of the day, no-one is any wiser as to how can some say 147A, some say 162A some say 240A (high current rating - expensive as hell from the UK), then they all start "googling" because even they aren't even sure anymore - and before you know it - you can run half of Eskom on a 35mm² Battery Cable ... 😆

 

Why on the AC side of things is this more common and straight forward, ie. ask them for 2.5mm GP Wire and almost all of them will tell you the exact same.

 

I understand with Battery / Welding Cable comes complexities like number of strands, insulation type, etc. but if I search for 35mm² Battery Cable, almost every supplier (some even selling the same cables are way out of bounds from any kind of "normality").

 

I'm trying to get to the bottom, not just of what is right (according to SANS), but also what is safe, ie. not trying to skimp on cable or such ~ but even a 25% over-spec leaving room for "additional" safety.

Edited August 19, 20224 yr by RabidBunny

1 hour ago, Scorp007 said:

Selecting a 35mm welding cable that is good for 220A at 100% duty cycle would be fine.

That's my gut feeling as well ...

1 hour ago, Scorp007 said:

Interesting you mention SANS 1574 as well as 400V for welding cable. My specs indicate a maximum of 100V to earth.

Original post did refer to SABS ... 😀

Most Welding Cables run 400V+ easily ... many of them rated for 1000V (max 2000V)

7 minutes ago, RabidBunny said:

That's my gut feeling as well ...

Original post did refer to SABS ... 😀

Most Welding Cables run 400V+ easily ... many of them rated for 1000V (max 2000V)

I wouldn't know. Just looking at the specs.

AC house wiring is old just sold as per the SANS-10142 ratings. Because, ultimately, some sparky has to sign off the CoC, and if it is not SANS-10142 spec, he will want to see full manufacturer data sheets and SANS certificates before he signs it.

The same applies to DC house wiring, so if you vary from the SANS-10142 current ratings, your sparky is going to want proper evidence that the wires are up to spec.

For general industrial wiring, the specs vary wildly.  I have browsed a few, and they all have different specs based on intended application. Some allow for higher conductor temperatures. Some have time limits at max load, some use lower ambient temperature.  You need to read the datasheets very carefully to make sure that it will actually apply to your installation (and be prepared to prove this to your sparky).

3 minutes ago, Scorp007 said:

I wouldn't know. Just looking at the specs.

I'm with you on this one, even those guys specs say Battery Cable 35mm² can handle 220A at 100% duty cycle; hence the confusion as I'm trying to avoid installing 95mm² cable at the price of half the system, where 35mm² proper Welding Cable (as per the above) will suffice (even for sanity sake 50mm² being half the price of 95mm²).

14 minutes ago, RabidBunny said:

I'm with you on this one, even those guys specs say Battery Cable 35mm² can handle 220A at 100% duty cycle; hence the confusion as I'm trying to avoid installing 95mm² cable at the price of half the system, where 35mm² proper Welding Cable (as per the above) will suffice (even for sanity sake 50mm² being half the price of 95mm²).

Power panel flexible cable in 35sq mm only good for 125A as per this table. Also higher voltage drop.

Same source as previous welding cable.

Edited August 19, 20224 yr by Scorp007

@Scorp007 ... yes, but compare theirs with their Welding Cables, and you'll notice a sizeable difference, that's why I'm leaning towards Welding Cables rather than Battery Cables ...

 

Edited August 19, 20224 yr by RabidBunny

I have recently been looking at this topic lately and have come to find there is no fix standard for vendors to adhere to which leads to wildly different specs. If you need to meet a standard/regulation for your install, use that as the guide line as Justin suggested. If not, let your budget decide the best mm2/meter per rand product.

Basically, physically only the total copper section determines the current carrying capacity. However the insulation temperature resistance determines at what temperature you can charge a conductor permanently. It depends also on environment temperature and cooling effects. I installed 25mm² welding cables.

However there is another issue not discussed yet. That's short circuit resistance. Consider the instant power available from a battery pack of 100Ah or even several in parallel. The cables must to be able to carry the short circuit current to trigger a breaker or fuse before blowing up themself. My four packs are each factory fitted with a 125A breaker. Then I have a 125A high power fuse in the collector line to each inverter. Personally I have more trust in fuses than in breakers, since almost all breakers on the market are conceived for AC. However DC is much more difficult to cut than AC. Fuse elements are inbetted in quartz sand that immediately fills the space of a melted element.

My gutt tells me your cable rating for continues use can easily take 3 or more times the current without getting to a point of danger. There should be minutes at this level to allow the fuse to pop or the MCB to trip. Do a trail with 0.5/0.75sq mm and see what current can flow.

DC MCBs should be different to AC and have blow out properties. Not so sure that branded DC MCBs are based on AC designs?

2 hours ago, Scorp007 said:

My gutt tells me your cable rating for continues use can easily take 3 or more times the current without getting to a point of danger. There should be minutes at this level to allow the fuse to pop or the MCB to trip. Do a trail with 0.5/0.75sq mm and see what current can flow.

DC MCBs should be different to AC and have blow out properties. Not so sure that branded DC MCBs are based on AC designs?

I checked the breakers on my battery packs: They are marked 250V/50Hz. Thus definitely AC breakers.

Fuse characteristics: (HRC stands for High Rupturing Capacity.)

It shows that it takes about 5 times rated current to blow a fuse in half a second. At one second the curve almost levels out at 200% rated current. As a matter of fact it takes approx 20 minutes to blow a fuse at 150% rated current. Breakers are designed to imitate fuse characteristics. However the bi-metal element is too slow on very high currents, therefor the magnetic tripping intervenes.

23 minutes ago, Beat said:

I checked the breakers on my battery packs: They are marked 250V/50Hz. Thus definitely AC breakers.

Fuse characteristics: (HRC stands for High Rupturing Capacity.)

It shows that it takes about 5 times rated current to blow a fuse in half a second. At one second the curve almost levels out at 200% rated current. As a matter of fact it takes approx 20 minutes to blow a fuse at 150% rated current. Breakers are designed to imitate fuse characteristics. However the bi-metal element is too slow on very high currents, therefor the magnetic tripping intervenes.

Thanks for sharing. It's decades since I last opened a MCB to check and see if they have bi-metal (time) and magnetic trip elements. If as per your batteries I hope they do in fact trip.  I have tested some MCBs of a few production runs ago and found the AC type would not trip in an acceptable time. The even older Fuchs MCBs would trip spot on although also rated AC. I used a 5A one on a DC boost circuit from 12 to 24V and worked for years when it had to. It saved my boost module from over heating.

When cleaning up tabs I spotted this datasheet which could give you an idea just how tricky it is to (legally) use wire for off-label purposes:

When used as 'welding cable' the 50mm² cable meets the legal requirements to be rated for 280A. Exactly the same cable, when used for power supply or panel wiring, can only be legally rated at 196A.

Very interesting topic ! I am going a different path on research and that is if the cable is rated at 600V or more but is marked as Welding or battery cable can we use it for A.C ? My thought process is that copper is copper and DC cable is robust and insulated well so should hold to A.C.

This stems from retrofitting a DV and using very flexible DC cable with ferrules is a lot easier than wrangling with the equivalent 16mm GP wire

 

I have gotten as far as panel flex or powerflex but still cannot get an accurate data sheet.

 

 

 

11 minutes ago, Dylboy said:

Very interesting topic ! I am going a different path on research and that is if the cable is rated at 600V or more but is marked as Welding or battery cable can we use it for A.C ? My thought process is that copper is copper and DC cable is robust and insulated well so should hold to A.C.

This stems from retrofitting a DV and using very flexible DC cable with ferrules is a lot easier than wrangling with the equivalent 16mm GP wire

 

I have gotten as far as panel flex or powerflex but still cannot get an accurate data sheet.

 

 

 

Cable is cable and not is it AC or DC. What matters is the voltage rating. For PV systems it is normally only on the battery side as the inverter input/output we use GP type wiring in single or different cable composition.

If you need detail specs on flexible panel cable just give the size and I will look it up.

9 hours ago, Scorp007 said:

Cable is cable and not is it AC or DC. What matters is the voltage rating. For PV systems it is normally only on the battery side as the inverter input/output we use GP type wiring in single or different cable composition.

If you need detail specs on flexible panel cable just give the size and I will look it up.

Thought so, what gets me is how some have different ratings but I see now it may be due to temperatures:)

Do you look in the Sans 10142-1 book for the amp rating for size cable ? For example 16mm panel flex ?

2 hours ago, Dylboy said:

Thought so, what gets me is how some have different ratings but I see now it may be due to temperatures:)

Do you look in the Sans 10142-1 book for the amp rating for size cable ? For example 16mm panel flex ?

No I refer to the tables from a manufacturer. The best test is still to check during use. Most problems and fire does not start from cables popping or burning due to heat but from hot connections at terminations.

Do a regular check especially on battery and inverter due to the very high currents they are subjected to. Connections do require regular maintenance.

Talking battery cables reminds me a story:

Years ago a bought from Game a set of nice thick automotive battery jumper cables, guaranteed 200A. When it came to the emergency application they failed to start my engine. They only provided some charging current to my battery so I could after a while start the engine from my battery. I got suspicious and opened up one of the clamp handles. What I found was outrageous. The nice thick cables consisted of 99% insulation and just 1.4mm² copper. That copper was not even crimped to the clamp but only squeezed between the clamp and the insulation. I brought it back to customer service and got refunded. By the way, Midas sold the same product.

I then bought 6m of 16mm² welding cable and soldered 3m each to the clamps. I could start with them a 2l diesel engine from a 50Ah battery.

nn