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jokani avatar image
jokani asked

Multiplus Grounding Connection Wire Size

Hi,

Multiplus 12-3000-120 intsalled in a boat, the DC current carying cables are 95mm2.


ABYC Notes:

1708537075350.png


Can I apply the exception and use a 50mm2 grounding cable, or would it need a 95mm2 cable?

As the stud is only 6mm, I'm hoping a 50mm2 will suffice.

TIA


Multiplus-II
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Charlie Johnson avatar image Charlie Johnson commented ·
This is sticky because of the AWG/metric designation of cable.

Note: the ampacities below are presented as outside machinery space/inside machinery space

  • AWG 1/0 equivalent is 53.5mm^2: Ampacity 199.5A/169.6A
  • AWG 2/0 equivalent is 67.7mm^2: Ampacity 231.0A/196.4A
  • AWG 3/0 equivalent is 85.2mm^2: Ampacity 269.5A/229.1A
  • AWG 4/0 equivalent is 107mm^2: Ampacity 311.5A/264.8A

Your installation used a B+ cable between 3/0 and 4/0. You will have to use 4/0 cable to be compliant. However, if you fuse the B+ at 199.5A/169.9A you will comply with ABYC but will not be compliant with the Victron Manual that specifies a 300A fuse.




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jokani avatar image jokani Charlie Johnson commented ·
Brilliant, thanks Charlie
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jokani avatar image jokani commented ·
Unsure why there is not an option to select this as the answer.
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1 Answer
amcarter333 avatar image
amcarter333 answered ·

I have a Multiplus 12-2000-120 on my boat. In a recent boat survey, we received a "Priority Issue" report regarding the size of the DC positive cable between the batteries and inverter. It said: "The chassis DC Positive cable is too small on the inverter and lacks a fuse in this cable between the batteries and inverter. Recommendation: current ABYC standards indicate that the chassis ground cable should be the same size or one size smaller than the DC cables and should have a suitably rated Class T fuse and fuse holder for adequate ampere interrupting capacity (AIC) rating and for rapid tripping response to protect the inverter. This is to ensure that the large DC inverter fuse will trip in the event of a short rather than the smaller AC safety ground and chassis ground cables overheating/burning."

To remedy this issue, we hired an electrician to replace the original smaller DC Positive cable with a 4/0 cable between the Multiplus. He installed a FUSE BLOCK CLASS T 225- 400A in this cable with a FUSE AT3/CLASS T 300A

Hope this helps.

.

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Charlie Johnson avatar image Charlie Johnson commented ·

"Recommendation: current ABYC standards indicate that the chassis ground cable should be the same size or one size smaller than the DC cables and should have a suitably rated Class T fuse and fuse holder for adequate ampere interrupting capacity (AIC) rating and for rapid tripping response to protect the inverter. This is to ensure that the large DC inverter fuse will trip in the event of a short rather than the smaller AC safety ground and chassis ground cables overheating/burning."

The surveyor is incorrect in his finding. There is no requirement for a Class T fuse for the B+ in the Standards. In fact, if you search the Standard for "Class T" you will find zero instances.

BTW, 4/0 cable has an ampacity of 311.5A outside of machinery spaces and 264.8A inside machinery spaces. If your I/C is in a machinery space, the 300A fuse is not appropriate for the 4/0 B+.

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