[RE-wrenches] single string of batts: must the interconnects be inverter size cables?

[Phil Undercuffler]

The interconnects are part of the circuit.  Typical flexible cables used
with batteries are THW rated (75C column), so in free air 2/0 interconnects
would be good for 265 amps, before any temperature derates.  Therefore,
you'd be safe from a NEC point of view.  However, if the inverter
manufacturer has recommended 4/0 cables, then that recommendation would
apply to all cables in the circuit.  Battery based inverters are asked to
surge many times their rated capacity -- a 24V 4kW inverter surging to 2x
capacity (pretty normal circumstances) is going to draw over 360 amps (8,000
/ 22), even if only for a short period of time.  You don't want your
interconnects to be the weak link in the system, causing shutdowns due to
undervoltage unnecessarily.

I'd use 4/0.

Phil Undercuffler
Conergy





On Fri, Feb 19, 2010 at 12:01 PM, Mick Abraham <mick at abrahamsolar.com>wrote:

> Example: 12 two volt battery cells in one 24 volt string. 4kW
> inverter/charger has 250 amp DC breaker size and 4/0 cables...as the
> inverter folks would want.
>
> So...do the "cell to cell" interconnect cables have to also be 4/0? In the
> example above, 2/0 interconnects would suffice from the standpoint of basic
> safety...and even from the voltage drop standpoint...right?
>
> Inverter company people may be best qualified to answer this, but any
> replies will be appreciated. While I'm at it: do the inverter folks request
> oversize cables because they want more capacitance on the DC input...or
> what?
>
> Jolliness,
>
> Mick Abraham, Proprietor
> www.abrahamsolar.com
>
> Voice: 970-731-4675
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