PV Junction Box: purpose and connection

A photovoltaic (PV) junction box is an important part of the solar panels. The junction box is an enclosure on the module where the PV strings are electrically connected.

Solar panel PV junction box — Solar panel (PV) junction box

The majority of junction box manufacturers are nowadays based in China.

Junction box sunlont — PV junction box, manufacturer Sunlont (one of the early and experienced junction box suppliers in Shanghai)

How is the junction box connected to the solar panel?

A PV junction box is attached to the back of the solar panel (TPT) with silicon adhesive. It wires the (usually) 4 connectors together and is the output interface of the solar panel.

Ugly looking silicon around PV junction box — Ugly looking silicon around solar junction box

How to connect the solar panel junction box to the solar array?

With the use of a junction box, it becomes easy to connect the solar panel to array. Usually cables with MC4 / MC5 connectors at the end are used.

A good junction box keeps corrosion at the terminals to a minimum, as it will exclude water coming in.

PV junction box with MC4 compliant connectors

When purchasing solar modules, always have a look at the IP rating of the PV junction box. A completely water tight junction box carries IP 67.

How does the PV junction box protect the solar panel?

Most photovoltaic junction boxes have diodes. The function of the diodes is to keep the power flow going in one direction, and prevent power from feeding back into the panels when there's no sunshine.

Inside and opened PV junction box — Diodes inside and opened junction box

A quality PV junction box is certified (e.g. via TÜV) and regulates the heat and offers reliable long-term safety.

graeme

on 23 Jan 2023

Rather than use a Y connector to run two solar panels in parallel, can I join both positive cables together/neg together within a single junction box, with the cable that runs to the solar regulator? 160W panel for RV? Thanks

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Santhosh

on 25 Jul 2022

Is it technically possible to have this Junction box away from the panel (to reduce panel height of flexible panel)? e.g. a wire (1.5 meter) to an external Junction box unit which combines 6 such panels.

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Neil

on 29 Sep 2015

Can you recommend any reliable junction box brands? And is nowadays an IP67 rating a must? Thanks, Neil.

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Stella

on 08 Jun 2016

Hey, Neil, if you are interested in junction box, please have a look at our website; we are a leading enterprise specially engaged in PV junction box, connector and cable used for solar PV module. Or you can contact me @ suncheng@renhesolar.com.

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Dricus

on 02 Oct 2015

For the IP rating of junction boxes, IP65 is still a common standard. I'd say: why not require the highest (IP67) standard? Pricing is similar..You can explore the difference between IP65 and IP67 junction boxes here: https://sinovoltaics.com/learning-center/components/iec-529-ip-65-ip-67-solar-junction-boxes/Leading brand examples are for example Tyco and Shoals. They're known to be of high quality. However there are dozens of Chinese brands that now offer fully certified and reliable PV junction boxes as well.Junction boxes aren't rocket science, basically they're a couple of diodes in a plastic box ;)

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Ncraju

on 21 Feb 2016

Can you help me understand (project report/web link) on the manufacturing process of the junction box Or a DPR on manufacturing junction boxes

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tushar vasani

on 31 Aug 2016

any buddy tell me which type certification required for solar pv junction box like tuv but coddind please

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Rick A Moore

on 07 Sep 2016

The PV Junction Box I am using is similar to this one, but is manufactured by Amphenol. When I connect my solar panel to it using the first (negative) and fourth (positive) bars, it shorts out the panel. What is the correct way to connect it to my panel? My panel is 36 cells with single negative and positive leads. Panel is generating 23 to 23.5 volts when testing the bare leads (not connected to the JBox. First bar (negative) is the one on the left when the Jbox cables are going downward. Please advise.

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amrendra

on 29 Nov 2016

Can we connected new pv junction box after burning old junction box

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sudhakar veerasamy

on 14 Jul 2017

Hai...what kind of diodes are used in junction box?bypass diode or blocking diode?

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Dricus

on 14 Jul 2017

Solar junction boxes have bypass diodes.Blocking diodes are typically used to prevent batteries from discharging backwards through your solar panels at night.

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Victor Prado

on 17 Feb 2022

Dear Dricus, I'm confused. The bypass diodes aren't used to isolate the shadowed solar panel in the array? However, the solar junction box diodes and solar panels are connected in series. So, the solar junction box diodes aren't blocking diodes ? Thank you for your assistance !

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