Following a change to the solar standard relating to disconnection points, it is important for installers to know the risks and ensure their correct handling, writes Michael Shaughnessy, technical program specialist and policy advocate at the Clean Energy Council.
A rewrite to solar standard AS/NZS 5033, published in late 2021, came as a relief to many people in the solar industry. It allowed solar designers and installers to finally do away with much-maligned rooftop DC isolators under certain circumstances.
Rooftop DC isolators and their cousins adjacent to the power conditioning equipment (PCE) have been responsible for many solar system fires. The problem is almost always water ingress. Once water causes a photovoltaic DC short circuit positive to negative, the resulting arc will not extinguish until the sun goes down or a competent person intervenes.
Disconnection points were introduced into this version of AS/NZS 5033:2021 as a method of PV array isolation and can be used instead of rooftop DC isolators as long as PV DC cables do not pass within 600mm above the ceiling when installed more than 1.5m from an external wall. Where there are more than two strings in parallel in an array, to maintain the ability to use disconnection points, string fusing shall be installed on the strings or the strings shall be paralleled at an additional load break disconnector, external to the inverter.
Disconnection points or similar methods of “rooftop” array disconnection are common in other parts of the world, but there is risk with any rule change. The risk here is that installers will not heed the requirements of the standard and disconnection points will be installed in an unsafe way or in a location where they cannot be readily accessed for disconnection. Below are some of the key risks of disconnection points and advice to ensure correct installation.
Risk 1: Mismatched Connectors
Plugs and sockets (sometimes called MC4 connectors) put together that are not of the same make and model will not have the current carrying capacity stated. This can lead to connectors melting, and potential arcs and fires.
Connectors should also be correctly selected for the cable diameter to maintain IP rating.
Risk 2: Poorly fit off connectors
Connectors shall be fit off using the correct tool for crimping pins and tightening nuts. Incorrectly crimped pins can result in a lower current carrying capacity than stated. Connectors without the nut correctly torqued onto the cable insulation can lead to water ingress, corroding pins and can cause arcs.
Risk 3: Positive pair and negative pair of connectors not co-located
The positive pair and negative pair of connectors shall be located together so they can be disconnected in close succession and ensure both legs of the one string will be disconnected.
Getting this wrong could cause confusion or provide a false sense that a faulty string has been isolated when in fact it has not.
Risk 4: Disconnection point unreachable
Disconnection points shall be readily available from on the roof and not be more than 150mm under the module. Disconnection points that are too far under the modules or secured with stainless-steel cable ties instead of stainless-steel clips may be too difficult to access and put the person wishing to disconnect in danger.
Risk 5: Incorrect labelling
DPs shall be labelled in at least three places.
- All the isolation points shall be detailed on the PV site plan at the switchboard and/or meter panel.
- A label on the side of the module or structure within 300mm of the disconnection point to draw a person’s attention: “WARNING – PV string disconnection point”.
- A label on the positive and negative cable within 100mm of the disconnection point: “WARNING – Loads must be isolated and circuit must be tested for the absence of current before unplugging”.
Labels must not impede the ability to disconnect the connectors.
Poorly located or missing labels could lead to a person not being able to find a disconnection point or forgetting to test for no current flow before disconnecting.
The Clean Energy Council has noticed instances of all the above non-compliances in the field after the first year of implementation. The most commonly identified non-compliances relating to DPs is mismatched connectors and the positive pair and negative pair not being together. There have been instances of fires started by mismatched connectors at DPs. Levels of compliance should increase as installation best practice becomes more ubiquitous in the industry.
Paralleling of DPs
A disconnection method, either load break disconnector or DP, shall be installed adjacent to its array. It is possible to use a DP as the disconnection method for an array of two strings in parallel that are not co-located using appropriately rated branch connectors, sometimes called “y connectors”. This is only possible for arrays of two strings.
When there are more than two strings in an array with DPs, the paralleling shall occur at the PCE load break disconnector. If the strings have string fusing, this may be an inverter integrated isolator. However, if the strings do not have string fusing, an additional load break disconnector shall be installed external to the inverter.
Get expert support from Michael Shaughnessy and the rest of the Technical Services team at the Clean Energy Council with a myCEC subscription. Find out more at cleanenergycouncil.org.au/industry/introducing-my-cec.