Mark Leslie Anderson is on trial in the ACT Supreme Court, having pleaded not guilty to assault occasioning actual bodily harm, trespassing, threatening to kill and breaching a protection order.

Anderson was accused of assaulting his former wife, Catherine Green, with a weapon he constructed using an electrical cord and metal at a home in Farrer in June 2010. When the device failed to deliver a shock, he was alleged to have used the cord to choke her and his hand to try to suffocate her.

On Thursday, Chief Justice Higgins dismissed an offensive weapon charge as there was no evidence the cord had been connected to a power source. The judge said the cord was not a weapon unless it could produce an electrical current.

Anderson, giving evidence in his defence on Friday, said he had gone to the home - despite the protection order - at his ex-wife's request to fix some electrical wiring.

''I concede I shouldn't have been there but I feared for the safety of my children,'' he said. ''That was in my mind.''

Asked to elaborate, Anderson said he was afraid one of the children might come into contact with live electrical wires. He said he did not know an electrician who could do the work and he had no money because of family law battles.

''I knew it would be a quick fix, I could do it, so I decided I would do it,'' he said.

Anderson also denied putting his hand over Ms Green's mouth and nose so she had trouble breathing and denied locking his fingers around her throat.

The defendant also said he had never before been charged with a criminal offence and, during his years on the force, was never the subject of a disciplinary charge.

The trial before Chief Justice Higgins continues on Monday.